Shimano vs. SRAM

We often get asked, "What's the difference between Shimano and SRAM?" It's a common question people have when shopping for a new bike, and there are plenty of opinions. The answer isn't at all straightforward. Both companies offer a range of products that work well and offer comparable performance.
So how do you decide which is right for your bike?
Shimano and SRAM are the two dominant component manufacturers in the cycling industry, and the vast majority of modern bikes are going to come with one of their drivetrains. Some riders tend to be more loyal to one brand over the other based on personal experiences. Others have specific ergonomic preferences. For ultra-picky riders, choosing between bikes built with Shimano or SRAM can be a major factor in their purchasing decisions.
In this story, we can't definitively answer whether one is “better” than the other (sorry). Instead, This comparison aims to shed light on the similarities and differences between the two brands and their products. The more you can learn about what drives your bike, the easier it will be to make informed decisions about where your loyalties and what products are right for your ride.
Note: Campagnolo is a third option for bicycle components. However, it makes up a very small percentage of total new component sales when compared to Shimano and SRAM. Plus, it only makes road components. For the average rider, the vast majority of bike options stick to Shimano or SRAM products, so that's why Campagnolo is not included in this piece. 

History and Mission

Shimano

The Shimano story begins in 1921, almost 100 years ago, in Sakai, Osaka, Japan. Shimano’s founder, Shozaburo Shimano, was only 26 years old when he moved into a small rented space in a demolished celluloid factory and opened Shimano Iron Works. With a borrowed lathe, Shimano’s ambitious goal was to produce his first bicycle component: freewheels.
Shozaburo Shimano | Photo Courtesy Shimano
At the time, freewheels were the component that took the most technology to produce. Shimano, however, was so confident in the reliability of his freewheels that he backed them with a bold guarantee — any defective freewheel would be replaced by two.
The original Shimano freewheel | Photo Courtesy Shimano
Shozaburo Shimano led his company and developed bicycle components until his death in 1958. His son, Shozo Shimano, took over as the next president. Over the next 50 years, Shimano grew to become the world’s dominant component manufacturer, overtaking former leaders like Campagnolo and SunTour.
Shozo Shimano (left) at Shimano American Corporation office in New York - 1965 | Photo Courtesy Shimano
With high quality and reliable products, Shimano has established itself as a benchmark component brand in the industry. It is currently led by Shozaburo’s grandson, Yozo Shimano. With sales that constitute an estimated 70-80% of the global cycling component market by value, it is the biggest cycling component manufacturer in the world. Their stated mission is to promote health and happiness with outdoor products that help people enjoy nature and the world around us.
Annual Revenue: $2.3 Billion (reported 2017)
Employees: 11,829
Philanthropy: Shimano is one of the founding members of the EcoMobility Alliance, an international partnership of people and companies that work to improve EcoMobility.

SRAM

SRAM’s unique name is said to be an amalgamation of the names of its founders. It comes from combining letters from Scott, Ray, and Sam (Ray is the middle name of former CEO, Stan Day). Scott King was the company's attorney. Stan R. Day was SRAM’s first CEO. And Sam Patterson was an engineer and designer who created SRAM’s first product.SRAM's founder and first CEO, Stan Day | Photo Courtesy SRAM
SRAM was founded in Chicago, Illinois, in 1987. The company began with a single product — the Grip Shift. The Grip Shift was an indexed gear shifter that wrapped around the ends of drop handlebars. Traditionally, riders had shift levers mounted to the frame, but Grip Shift allowed riders to change gears without removing their hands from the handlebars. Sam Patterson, who at the time worked for an engine manufacturer, designed SRAM's first product.
Early Grip Shift on a drop-bar bike | Photo Courtesy SRAM
With a belief in the power of the Grip Shift, Stan Day assembled investors, set up an office, and became the company’s first president while Sam Patterson became the head of research and development. Over the next 30 years, SRAM acquired several component companies, such as RockShox, Zipp, Truvativ, and Quarq. This growth has led it to become the second-largest component manufacturer in the world with an expansive catalog of bike parts.
One of SRAM's key goals is to be the most exciting component manufacturer in the industry. It has worked toward this goal with innovative products that have produced notable shifts in the industry. A point of pride for the company has been its success in taking on Shimano, who once controlled well over 85% of the cycling component market.

Annual Revenue: $725 Million (reported 2017)
Employees: 3,500
Philanthropy: World Bicycle Relief (WBR) is a non-profit that specializes in large-scale, comprehensive bicycle distribution programs to aid poverty relief in developing countries.

Key Technological Innovations

Both Shimano and SRAM have developed products that have moved cycling forward. Much of the bike technology we take for granted today is the result of Shimano's and SRAM's innovations. Here are a few key products they've developed that have helped shape modern cycling.

Shimano

1984 - Shimano Index System (SIS)
The Dura-Ace 7400 group introduced indexed shifting, which provided accurate gear changes with shifts that corresponded to clicks in the shifter. Gear changes became more precise and faster as riders could select the gear without having to fiddle with the position of a friction shifter. Indexed shifting is the basis for how modern mechanical shifters work.
1989 - Shimano Total Integration (STI) / Rapid FirePhoto Courtesy Shimano
STI is a shifting system that allows cyclists to shift gears, operate the brakes, and steer without removing their hands from the handlebars. STI integrated shift levers into the brake hoods, creating the blueprint for modern road, cyclocross, and gravel bike shifters as we know it. Rapid Fire was a flat-bar version of STI, using a pod with trigger style levers clamped to the bar. Trigger-style shifters are now the most common type of shifter used on mountain bikes.
1990 - Shimano Pedaling Dynamics (SPD) shoes and pedals
Shimano created a standard-setting clipless shoe and pedal system. Many brands now produce pedals compatible with Shimano SPD style cleats. It is one of the most ubiquitous clipless pedal systems.
2009 - Digital Integrated Intelligence (Di2) electronic shifting
Di2 was introduced for Shimano’s Dura-Ace level group and was the first commercially viable electronic shifter and derailleur system. Di2 made electronic shifting the new standard for top-of-the-line group.
2014 - XTR Di2
Shimano brought its Di2 technology to mountain bikes with the XTR Di2 M9050 group, the first electronic mountain bike group.

SRAM

1987 - Grip Shift
SRAM's story began with an indexed gear shifter that wrapped around the handlebars. The Grip Shift design still sees use today on some mountain bikes, commuters, and other flat-bar bicycles.
2006 - DoubleTapPhoto Courtesy SRAM
SRAM’s integrated shifting solution for road bikes allowed the rider to shift in both directions using a single shifter paddle. This was also SRAM's first foray into producing a complete road component group, Force.
2012 - 1x11 XX1 group
Riders had experimented with 1x (pronounced “one-by”) drivetrains in the past, but XX1 was the first 1x drivetrain from a major manufacturer that became a mainstream option. Like previous attempts at single-chainring drivetrains, XX1 simplified shifting by removing the front derailleur. This configuration is now the standard for most mountain bikes and is popular on cyclocross and gravel bikes as well.
2015 - Red eTap
eTap was SRAM’s first electronic road group and it set itself apart from Shimano’s Di2 system by being wireless.
2016 - 1x12 Eagle group
Eagle was the first 12-speed mountain bike group. It expanded the capabilities of SRAM’s already successful 1x11 groups with a wider 500% gear range that was comparable to traditional 2x systems.
2019 - eTap AXS and Eagle AXS
SRAM continued the progression of its wireless electronic group with AXS. AXS introduced a new 12-speed road bike group and the first wireless electronic mountain bike group.

Component Differences

Shimano and SRAM have been competing for the last 30 years. Competition has bred many fantastic cycling components. This section covers some of the key tech and design differences in certain Shimano and SRAM components.

Shifters

STI vs DoubleTap

Shimano and SRAM road bike shifters use different lever designs to accomplish upshifts and downshifts. Shimano's STI shifters separate the control of up and downshifts into two different shift levers. The brake lever itself pivots inward to act as an up/downshift lever, and a second paddle-shaped lever sits behind it to shift in the other direction.
Instead of two separate levers, SRAM's DoubleTap uses a single paddle-shaped lever behind the brake lever (which is fixed) to handles both up and downshifts. Pushing this lever one click inward shifts the drivetrain in one direction. Pushing the lever further in, past the first click, causes the drivetrain to shift in the opposite direction.
Both shifter designs are simple and intuitive once a rider has learned how to use them. Both designs also have the capability to downshift multiple gears in a single lever stroke. Choosing between the two will often come down to rider preference and ergonomics.
Some riders also tend to be picky about the shape of the shifter hoods (the rubber area on top of the shifter where the rider places their hands). Shimano and SRAM both offer a variety of hood shapes and finding the ideal one may require some experimentation.

Rapid Fire Trigger Shifters

A Shimano XTR trigger shifter — the upshift lever (bottom) can be activated in either direction.
Both Shimano and SRAM offer trigger-style shifters for mountain bikes. Two shift levers are housed in a pod attached to the underside of the handlebar. This is the most popular shifter style for modern mountain bikes. Both Shimano and SRAM trigger shifters have the capability of downshifting multiple gears with one lever stroke.
The main difference in function is that Shimano's Rapid Fire trigger shifter features "2way-release," which allows the upshift lever to move in both directions. This means upshifts can be performed both by pushing the lever with the thumb or pulling it with an index finger. Again, it comes down to rider preference whether this feature is valuable. Riders used to pushing with their thumbs for both up and downshifts will be able to transition between Shimano and SRAM shifters without much thought.

Crank Arms

Crank Arm Material

Shimano is known for its Hollowtech crank arms. Hollowtech refers to a hollow, aluminum crank arm, generally made from two halves joined together. It maintains the stiffness of a solid crank arm while significantly decreasing the weight.
For its higher-end crank offerings, SRAM uses carbon fiber. Carbon fiber is made from carbon sheets and fibers bonded in resin. It has a higher strength-to-weight ratio than steel.

Both materials and crank designs perform well. Carbon is currently more common for high-end cranks. Shimano is one of the few manufacturers that sticks to aluminum. It claims the Hollowtech II design offers the same performance as carbon with greater durability.

Spindles

Both brands use their own spindle designs. Shimano uses Hollowtech II, which is a 24mm spindle. SRAM uses GXP, BB30/PF30, and DUB. The advantages and disadvantages of the different spindle designs can be debated to death and it's a topic that will require its own article. In general, a crank from any brand will require a specific bottom bracket to be compatible with both the frame and crank arm spindle.

1x Drivetrains

SRAM brought 1x drivetrains into the mainstream with its innovative XX1 group. Single-chainring drivetrains are now the most popular option for modern mountain bikes because of their increased simplicity and reliability. These drivetrains have even found a place on many cyclocross and gravel bikes.

Shimano initially resisted the move to 1x drivetrains, believing that more traditional 2x (“two-by”) drivetrains provided a more usable range when riding off-road. Shimano was able to eliminate many of the issues mountain bikers had with front derailleurs (e.g., vague feeling shifting, dropped chains, unreliable performance) with its side-swing front derailleurs.
These front derailleurs used a revised cable pull design to greatly improve performance, but it did little to stop the rise in popularity of 1x drivetrains. 2x mountain bike drivetrains are still available from Shimano but it has since developed more 1x drivetrain options remain competitive.

The downside for some riders using 11-speed 1x drivetrains is the reduced gear range. The release of SRAM’s 12-speed Eagle 1x drivetrains in 2016, addressed this by introducing an ample 500% gear range that has largely eliminated this issue. Three years after the release of Eagle, Shimano also released its first 12-speed mountain bike group, which provided a slightly larger 510% range.

Cassettes and Freehubs 

PowerdomeX

A 10-42t SRAM XX1 PowerdomeX Cassette 
SRAM's latest high-end cassette design is called PowerdomeX. These cassettes are constructed as a connected dome of cogs all machined from a single block of steel. This greatly reduces weight. The trade-off, however, is that these cassettes are far more expensive than a traditional cassette.
Shimano generally still uses the traditional cassette design with individual cogs stacked and separated by spacers or attached in clusters to aluminum carriers. SRAM’s lower-end XD Driver-compatible cassettes use individual cogs connected with pins in the same PowerdomeX layout. These are less expensive but heavier.

Proprietary Freehubs

Shimano’s Hyperglide is the most common freehub design, with many brands making wheels and hubs with compatible freehubs. SRAM cassettes have traditionally used the same design. This compatibility allows riders to switch from one brand to the other without changing their wheels or hubs.
With the release of XX1 Eagle for mountain bikes, SRAM made the bold step of releasing its own proprietary freehub, the XD driver. The XD driver freehub was designed to fit the new PowerdomeX mountain bike cassettes which have a smaller 10-tooth cog. The XD Driver freehub has remained in use for SRAM’s current 12-speed Eagle mountain bike group. SRAM has also released a road version know as XDR, which is used for its 12-speed eTap AXS road group.
Shimano has released its own proprietary 12-speed freehub design, called Microspline. It is intended for its new 12-speed mountain bike group. Microspline is similar to XD Driver in that it allows the use of a smaller 10-tooth cassette cog, but its shape is fundamentally different. This means Shimano and SRAM’s 12-speed cassettes each require a specific hub and are not interchangeable.

Gearing

Riders should generally select their gearing base on their needs. A rider doing fast group rides and races will need more top-end while a rider doing lots of climbing or loaded touring will need more low-end. Many new drivetrains attempt to provide as wide a range as possible to handle a larger variety of terrain and riding styles.

X-Range vs. Traditional Gearing

Recently, SRAM has challenged the traditional gearing that's been used on road bikes for decades. The new eTap AXS 12-speed group uses an entirely new gearing system, X-Range. It is intended to reduce front shifting, allowing riders to stay in the big ring for longer. It does so by shrinking the chainring size compared to traditional drivetrains and using cassettes with 10-tooth cogs and smaller steps between cogs. Shimano currently still uses traditional gearing, which has seen great success over the years. Until X-Range, few riders had thought about changing their gearing. Only time will tell whether X-Range will overtake traditional gearing as the more popular gearing option.

Photo Courtesy SRAM
Traditional Chainring Options (teeth): 53/39, 52/36, 50/34
X-Range Chainring Options: 50/37, 48/35, 46/33

Traditional Cassette Options: 11-23, 11-25, 11-28, 11-30, 11-32, 11-34, 11-36
X-Range Cassette Options: 10-26, 10-28, 10-33

Cyclocross and Gravel Gearing

For cyclocross and gravel bikes, Shimano and SRAM offer several options. Both brands have drivetrains with traditional cyclocross gearing, which generally uses 46/36t chainrings paired with a traditional road cassette.

SRAM also offers 1x cyclocross and gravel drivetrains that use their mountain bike technology, as well as AXS drivetrains using SRAM’s new X-Range gearing.

Shimano’s new gravel-specific GRX group offers a couple new and unique 2x chainring options as well— 48/31t and 46/30t. These new gearing options have a large delta (the difference in tooth count between chainrings) which provide a much large gearing range for off-road riding.

Mountain Bike Gearing

On mountain bikes, SRAM's 11-speed XX1 drivetrain with its 10-42t cassette created a whole new generation of wide-range mountain bike cassettes. Shimano responded to SRAM with its own 11-speed 1x drivetrains using 11-40t, 11-42t, and 11-46t cassettes.
Then came the introduction of SRAM’s 12-speed Eagle drivetrain with a 10-50t cassette, which solidified the 1x drivetrain as the dominant option for mountain bikes. Shimano has responded with its own 12-speed drivetrain using a slightly larger 10-51t cassette. Chainrings that are commonly paired with these wide-range cassettes range in size from 28-36t.

Rear Derailleurs

Clutch Design

Shimano derailleurs intended for rough roads and off-road riding use its Shadow Technology, which slims the derailleur and keeps it pulled up out of harm's way. The GRX and mountain bike rear derailleurs use a friction clutch that keeps the derailleur in place on rough terrain to improve chain retention.
SRAM also uses a clutch on all of its mechanical 1x drivetrain derailleurs. A small difference between how SRAM and Shimano Implement clutches is that Shimano’s clutch mechanism can be toggled on and off. Turning the clutch off makes the derailleur easier to manipulate to remove the rear wheel. Instead of a toggle switch, SRAM uses a cage lock which locks the derailleur cage in an extended position for wheel removal.

SRAM Orbit Damper and Overload Clutch

Traditional derailleur clutches use friction plates and springs but the latest generation SRAM AXS derailleurs have a new hydraulic damper and hydraulic clutch system to provide chain retention. The Orbit Damper for road bike derailleurs prevents movement of the derailleur on hard jarring impacts to maintain chain tension on rough roads without the full lockout provided by a clutch. The Overload clutch for mountain bike derailleurs will maintain tension like a traditional clutch, but upon impact, it disengages a motor gearbox inside, giving the derailleur the freedom to move and protecting it from damage.

Electronic Drivetrains

For both Shimano and SRAM, electronic drivetrains are at the top of their component hierarchies. They represent the pinnacle of their drivetrain technology.

Shimano Di2

Shimano’s electronic Di2 (Digital Integrated Intelligence) drivetrain technology was first introduced in 2009 with the Dura-Ace Di2 group. It later trickled down into the more affordable Ultegra Di2 group in 2011. Di2 is only available in higher-end groups. Dura-Ace and Ultegra for road, cyclocross, and gravel bikes, and XTR and Deore XT for mountain bikes.

SRAM eTap, eTap AXS, and Eagle AXS

SRAM’s first electronic drivetrain, eTap Red, was introduced in 2015. This has been followed in 2019 with the introduction of its AXS group — eTap AXS and Eagle AXS — which build upon and improve the original eTap. Like Di2, AXS is only available for higher-end groups. eTap AXS for road, cyclocross, and gravel bikes is available in Red and Force. Eagle AXS for mountain bikes is available in XX1 and X01.

Wiring

The major difference between Di2 and eTap/AXS is the use of wires. Di2 is wired and requires routing of the wires through the frame and components to function. This may or may not be easy depending on the frame. Shifters and the rest of the system are connected by a junction box, often under the stem. Some bikes hide the junction box in the frame or handlebars, but that requires additional routing. Though it is more complicated, routing Di2 is usually only a one-time job. Once a bike is set up, it won’t need to be touched. eTap/AXS is wireless and transmits its signal using SRAM’s proprietary wireless protocol, Airea. The initial set-up is very quick and simple due to the lack of wires.

Batteries

Di2 uses a single rechargeable battery, which is often hidden inside the seatpost or handlebars. Older versions mount the battery externally on the frame. Di2 has 1,000-2,000km battery life. When it runs low, the front derailleur stops working first to preserve rear shifting. When the battery dies, the derailleurs will remain in the gear selected, essentially functioning like a singlespeed. Battery life can be checked by holding both shift button on the right shifter, which will activate an LED battery indicator light on the junction box.
eTap/AXS requires separate batteries in each derailleur which have approximately 20 hours of battery life. The rechargeable batteries are swappable between derailleurs if one runs low, meaning you can sacrifice the front derailleur battery to maintain shifting in the rear or vice versa. When the batteries die, the derailleurs will remain in the gear selected, essentially functioning like a singlespeed. Battery life can be checked by pressing the function buttons on the derailleurs, which will activate an LED battery indicator light on the derailleur. The shifters use common CR2032 batteries that usually last several seasons. Shifter paddles have an LED battery life indicator on the inside of the paddle.

Functionality

Di2 road shifters feature two shift buttons on each shifter. They essentially function the same as the up and downshift levers on STI mechanical shifters. eTap / eTap AXS road shifters have a single shift paddle on each shifter, similar to DoubleTap mechanical shifters, but they have a notably different function. The right paddle shifts the rear derailleur up into a harder gear, while the left paddle shifts it down into an easier gear. Front derailleur shifts are actuated by pressing both levers simultaneously.
The Di2 mountain bike shifter uses trigger-style shift levers similar to Rapid Fire shifters. It's notable that Di2 mountain bike shifters come programmed with the up and downshifts levers opposite of how mechanical Rapid Fire shifters are set-up. This can be reprogrammed if desired. Eagle AXS mountain bike shifters utilize a single large button that can move up or down to actuate shifts.
Both Di2 and eTap AXS have satellite shifters that can be placed in different areas of the cockpit. This allows riders to place shifters in areas where they will be easier to reach while climbing or sprinting. Both currently allow riders to use an app or software to customize the function of their buttons and shift action of their drivetrains. This can allow riders to change the function of specific buttons or adjust how much the drivetrain acts to aid the rider in proper gear selection.

Hydraulic Disc Brakes

Both Shimano and SRAM provide hydraulic disc brake options for all types of bikes. Disc brakes are already the standard for cyclocross, gravel, and mountain bikes, and they are slowly becoming more common on road bikes as well.

Brake Fluid

A major difference between Shimano and SRAM is their choice of brake fluid. Shimano uses mineral oil while SRAM uses DOT 5.1 brake fluid.
Mineral oil is hydrophobic, meaning it resists absorbing water from the air. The boiling points of mineral oil and DOT fluids are comparable, but the introduction of water reduces the boiling point and decreases performance. Being hydrophobic means mineral oil has a very long shelf life, and the boiling point will remain stable during the fluid’s lifespan. However, if any water does enter the braking system, it will pool at low points and compromise the whole system, requiring a full bleed. Mineral oil is non-corrosive, but it is also unregulated so manufacturers like Shimano determine the specifications of their own fluids and there are no minimum standards.
DOT fluid is hygroscopic, meaning it can absorb water from the air over time. As it does the boiling point will change. Because of this, open bottles of brake fluid have a limited shelf life so it’s often recommended to use opened DOT fluid within 12 months. The upside is that water won’t pool in a DOT fluid system and compromise it. DOT fluid is easy to clean, which is good because it is corrosive. It can damage sensitive surfaces on your bike as well as your skin and eyes. Because DOT fluid is regulated by the Department of Transportation, it’s governed by minimum standards that regulate quality and ensure it meets certain specifications. It’s also widely available, not just in bike shops.

Lever Design and Feel

Shimano and SRAM brakes also have a different feel from each other due to the technology they use at the brake lever.
Photo Courtesy Shimano
Shimano brakes use Servowave. With Servowave, initial pad travel is fast, so little lever movement is needed to contact the rotor. At contact, the power multiplication factor increases so more lever stroke is used to apply greater braking power. This allows the use of short, stubby MTB brake levers with less leverage and makes hydraulic road brake levers easier to pull from the hoods.
Photo Courtesy SRAM
Higher-end SRAM brakes use Swinglink, a cam shape inside the brake lever that reduces “deadband” while increasing progressive power throughout the pull.

When riders describe the difference in how Shimano and SRAM disc brakes feel, Shimano is often described as having more of an “on or off” or “lightswitch” feeling where the braking power comes on instantaneously. SRAM brakes will tend to have a more “progressive” feel which may be easier for some riders to modulate and control. Both styles work well and it often comes down to personal preference.

SRAM mountain bike brake levers are ambidextrous, meaning they can be swapped to either side of the cockpit without removing the hoses or rebleeding the system. This is beneficial to riders who need to switch which side their brakes are on. For example, I prefer to run my front brake on the right and have to swap every bike I ride. I often choose SRAM brakes to reduce the hassle.

Popularity

Because The Pro’s Closet is the world leader in buying and selling used bikes, we have substantial data about what bikes are popular and what group they are equipped with. I dug into our sales for the last 12 months and looked at thousands of different bikes to analyze how Shimano and SRAM are performing in different categories. The data presented below does not indicate that one brand is better than the other. It simply shows how bike manufacturers and owners have chosen to equip their bikes over the last few years.

Category	Shimano	SRAM
Road Bikes	76.0%	18.5%
Cyclocross / Gravel Bikes	51.1%	46.9%
Mountain Bikes	27.7%	71.5%

This data shows that, unsurprisingly, Shimano and SRAM make up over 90% of all bike groups we sell. Campagnolo is the next largest but only contributes to a small fraction of our sales.
The data also shows some recent trends. SRAM has become the dominant choice for mountain bikes, which is likely due to the increased popularity of its 1x drivetrains. Shimano, however, has maintained a firm hold on the road bike category, which it has dominated for decades. Cyclocross and gravel bikes are split fairly evenly between Shimano and SRAM. Neither brand has the advantage yet as the category is still evolving.

Final Thoughts

Shimano and SRAM both make quality products, but their approach and styles are different. Looking at the current component landscape, it can be said that Shimano is generally the more conservative of the two. Over the last decade, SRAM has pursued drivetrain innovation more aggressively. In many cases, Shimano has been forced to respond to remain competitive. A good example is the development of its new 12-speed 1x drivetrain in response to SRAM’s ground-breaking Eagle drivetrain. Time will tell if Shimano will react similarly to SRAM’s new eTap and Eagle AXS drivetrains. Shimano is not struggling by any means. It still remains strong in all categories, and many riders choose Shimano based on its long history in the sport and strong reputation for quality.

I’ve had the good fortune to ride more bikes than the average consumer. I’ve also known many co-workers who are very loyal to their chosen brand. For these ultra-picky riders, it often comes down to small subjective details like feel, ergonomics, and looks. I’ve swapped back and forth countless times.
I have SRAM on my personal mountain bikes, but Shimano on my road bikes. I may switch next season. 
Currently, my mountain bikes use SRAM Eagle drivetrains and SRAM brakes. They’re lightweight, perform well, and I can easily poach parts if something breaks. I also tend to prefer the progressive feel and ambidextrous design of SRAM mountain bike brakes.
For my road bikes, however, I usually go for Shimano Ultegra or Dura-Ace group. I prefer the function and feel of Shimano STI shifters and I like the shape of the hoods.
Up until last year, I had also exclusively ridden Shimano pedals which have always been smooth and reliable. But SRAM has yet to offer its own clipless pedal.
Your preferences are likely to evolve and change as you spend time riding one brand or the other. Shimano's new 12-speed mountain group and SRAM's new eTap AXS road group interest me, so next season I may switch things up. Many riders become accustomed to what they know and find it hard to switch brands. Others can jump back and forth without a second thought.
If you're on the fence, our suggestion is to just go ride both and change things as needed. Doing so can be logistically or financially difficult, but our Certified Pre-Owned bikes and Guaranteed Buyback Program are designed to make trying out great bikes easy. Where ever your loyalties lie, the important thing is that you’re on a bike that you love riding.