Let me leave out a few things like electronic vs. mechanical shifting and the like, and start by saying that you will be fine at the end with either drive train. It’s not like selling your Amazon IPO shares in 2001 or marrying the wrong person. So I’ll be a bit nitpicky.
Just for perspective, I have had several bikes with Shimano drive trains (MTB and road bikes), and only my latest bike features a SRAM drive train (Force eTap AXS). Although I have tried and demoed bikes with various SRAM and Shimano drive trains.
If you want to go with SRAM, one great option is a full Rival eTap AXS drive train with Red cranks. The Red cranks are super light and you’ll save >200 g.
There are a few things where SRAM is objectively better:
- More gearing options. SRAM is agnostic when it comes to 1x vs. 2x, and it offers a lot more natively supported gearing options. You can go from 10–26 to 10–52 with sufficiently many cassettes in between. Are there some gaps when you have particular needs? Perhaps. I’d like a 10–39 cassette, but overall you have lots of choice. 1x chain rings go from 36 till 50+ teeth, and with 2x you have lots of options, too. You can have larger range or narrower gaps, shift your gears towards the low or the high end, it is up to you. With Shimano’s 12-speed drive trains you have 2 cassette options.
- Related to that is component compatibility. Let’s say you would like to mix and match, but get the latest and greatest. With SRAM all 12-speed components are compatible with one another. You want an AXS dropper post on your drop bar bike? No problem. You want to couple your Rival eTap AXS rear derailleur to the Force-level 2x gravel crank? Sure. With Shimano that’s currently a nightmare. So you want an Ultegra Di2 drive train with GRX Di2 shifters (perhaps you prefer their hood shape)? Yeah, but only if you use the last generation of Ultegra Di2, no 12-speed for you. What about 1x on a proper road bike? Not with Shimano, you’d need to go third-party here.
- Shift logic. You will never miss a shift in the rear on SRAM. Never. (Also DoubleTap gels much, much better with me than Shimano’s mechanical shift levers.) It is simple, intuitive and requires no explanation. Even after two weeks, coming from a Shimano mechanical bike, I’d still misshift with the Di2 levers. It’s just bad design on Shimano’s part.
- Quark power meters. SRAM’s Quark power meters are just great. My DZero has just worked. I only had to change the battery once, that’s it. The Rival eTap AXS power meter is even cheap, cheaper than what I paid for my 4iiii crank arm-based power meter. In comparison, Shimano’s native crank-based power meters are known to be unreliable because of the crank design. (More specifically, the readings from the right crank arm are unreliable.) Perhaps this will be remedied with the latest 12-speed power meters, who knows. But Quark power meters are a known quantity and they are known to be excellent.
- The clutched rear derailleur is great. Perhaps you don’t need need a clutch, but just like with beefier brakes, it’s is just nice to have it even if you just need it once or twice.
- Wireless > cables & app. This isn’t just about setting the bike up. But SRAM has a much better app and doesn’t require an extra blip box. I know the new 12-speed drive trains no longer need those, but the loaner bikes with Di2 never had one so I couldn’t remap the buttons. Plus, of all the devices around you, how many still connect to others by cable? Is the number increasing or decreasing?
(Objective) advantages for Shimano
- I was really jealous of the extra buttons on the top of Shimano’s Di2 hoods, because I could change screens on my Wahoo with it — at least in theory since the loaner bikes didn’t come with the blip box.
- Battery life is longer, although to be honest, SRAM’s batteries are fully charged in <1 hour.
There are a few things which IMHO don’t matter at all:
- The 10-tooth cog/efficiency. Yeah, it is slightly less efficient, but I don’t think regular riders will notice this. And even if they do, the other advantages outweigh this by a huge margin.
- Weight. Weight is overrated, and I wouldn’t buy one over the other because you are saving 83 g.
- Mineral oil vs. DOT fluid. Both are fine. DOT fluid is corrosive, but don’t imagine what acid does to things in cartoons. Once set up correctly, both work and you won’t be able to tell.
- Rear shift quality and speed. Both eTap AXS and Di2 are fast enough, faster than Shimano mechanical (once you include lever throw). Perhaps Shimano is a tad faster but I found it made no difference when riding. My brain compensates for that. Both electronic groups sets shifted great. I don’t really like the whirring sound Di2 rear derailleurs make, but that’s the auditory equivalent of looks.
- Battery life/management. Yes, SRAM’s batteries are smaller, but they can be fully charged <1 hour and are easily accessible. I don’t think that’s a huge net advantage over Shimano’s larger Di2 battery.
- Tinging brakes. Maybe I got lucky and have found a great shop or the fairies of bike setup sprinkled pixie dust all over my components when they were mated to my bike, but I got a slight ting only once after a long, winding descent (> 500 m of elevation in one go with lots of bends and traffic). The ting only appeared towards the very bottom and disappeared after a few seconds.
- Looks aren’t as important to me. Some people find SRAM hoods ugly and wouldn’t want to buy one based on that. That’s not a criterion for me. Ergonomics is.
Subjective pros for SRAM
- I vastly prefer the hood shape and ergonomics of SRAM brifters. With Shimano the hump is not tall enough and too wide, so I couldn’t wedge myself in properly. With SRAM I can.
- Brake feel is better. I went from Shimano RS505 (105-level) levers and hydraulic disc brakes to Force eTap AXS. Although I have tried Ultegra-level brakes up until the latest 11-speed. I vastly prefer my SRAM brakes. The modulation is intuitive, I get more feedback and they feel less “wooden” if that makes any sense. SRAM hit it out of the park, I think.
- 1x friendliness. I hate Shimano for not giving riders the choice of whether they want to go 1x or 2x. IMHO the future is 1x with the exception of a few niches. That’s my opinion, and perhaps I am totally wrong, but at the very least 1x will become more and more common the more sprockets we have in the back. That’s just a fact.
Subjective cons for SRAM.
- I’d like to have an extra button on the hoods, and be able to e. g. toggle my lights or leaf through pages on my Wahoo.
Don’t knows
- Some people claim Shimano has superior build quality. I was very happy with my Shimano gear. Were there failures in the past, yes, but only very, very few. And what about SRAM? Well, I have my bike for only 6–7 months now, everything works fine, but ask me again in a few years.
- Front shifting. My road bike is 1x, so I don’t know about front shifting, an often cited weakness of SRAM drive trains. I hated Shimano’s front shifts already, and am glad I no longer have to deal with them.