If personal opinions count...
I much prefer Shimanos. I have Rivals on my gravel and like typical SRAM brakes, they don't compare well to Shimanos. I have Shimano on my MTB's.
Shimano are easier to service and maintain in my world.

 

No SRAM experience, but I have Shimano brakes on my road and gravel bikes. I'm happy with the power and modulation. I had no problems bleeding the brakes on my gravel bike (GRX) and that was the first time I've ever done that. That was starting with no fluid at all.

 

I have the original Ultegra (685) 11 speed hydro on my gravel bike and Force 11 on my cross bike. If the ergonomics were the same, I don't think I could tell them apart from the actual brake performance. They both engage and modulate predictably with lots of power. I prefer Shimano's shift action over SRAM, which combined with mineral oil vs. dot fluid would make them my pick, but on actual function of the brakes there's not much difference - both perform well.

 

I never liked my Rival 22 brakes, I'm not sure if I didn't get a good bleed or if they just are squishy. Comparing to GRX, I much liked GRX better, just like MTB brakes they had a harder bite point. But now I have Rival AXS and would say they are comparable to GRX, maybe not quite as hard bite point, but they are considerably stiffer feel than my mechanical Rivals.

 

there is an additional option:
swap your calipers to something like a juin tech GT-P / yokozuna ultimo
they are 4 pad hydraulic calipers that are cable pulled and are much much better than spyres or bb7's
you could then keep your drivetrain

i use those with rt-86 rotors and H03C pads and the result is really good
many reviews on the web mostly pretty darn positive

 

Also important to consider that GRX di2 has the pivot point moved way up so that braking in the hoods is way stronger than other levers

 

Great point. I find the GRX pivot point is perfect for riders who spend most of their time on the hoods. I wish Shimano would use this technology on their budget-minded groups like 105.

 

@Love Commander I spend as much time on drop bar bikes as mountain bikes, and hood ergonomics play as much a role in personal preference as the actual braking performance.

Bleed process: In general, I find SRAM's Bleeding Edge system slightly easier/quicker to bleed than Shimano. I also find SRAM's calipers weep less than Shimano.
Braking power: Both SRAM and Shimano have ample power and modulation for all road and gravel applications.
Ergonomics: I have medium hands and prefer the smaller hood shape of Shimano. I actually swap stems when switching a bike from Shimano to SRAM levers. (10mm shorter stem to compensate for SRAM's slightly longer hoods.)
Lever features: I prefer Shimano's Di2 shift lever layout to SRAM's eTap. I frequently use the auxiliary buttons on the top of Shimano's di2 hoods to toggle through my computer screens.

If you're going 1x and want to focus on singletrack performance, I would strongly consider Rival for 12-speed and more cassette/drivetrain combos, such as SRAM's "Mullet" drivetrain with a 12-speed mountain cassette.

 

Yup the repositioned pivot point on the grx di2 definitely makes a difference on the hoods. Shimano also has their clever “sissy” secondary brake levers on the flats. Brake bleeding with those can be a pia though.

 

Got Rival AXS on my road bike and GRX 810 on the gravel bike. While the braking feel is pretty darn close on each, I much prefer the GRX levers. Mainly because I can one/two finger brake from the hoods and still have my other fingers holding onto the hood under the lever. Can't do that with the Rival AXS levers, the shifter buttons mash my fingers when I brake.

 

I ride really long and steep and chunky NorCal fire roads on my gravel bike. When I bought my Diverge 2 years ago, I was pushing 230 lbs and the 2 piston Sram calipers were not cutting it. I got some Hope RX4 calipers (4 piston) that work with the existing levers whether Sram or Shimano, and they were a game changer. These things stop on a dime and have wonderful modulation from the hoods. Now that, I've lost 40 lbs, I have to a more refined braking technique, but I won't be giving up 4 piston performance.

 

Thanks for the input everyone! This has been really helpful. I'm kind of leaning toward the GRX, if anything than to try something new. But the mention of on-hood braking leverage sounds appealing.


I probably should have mentioned I'm currently pushing 210lbs (down from 235!). On my way back to my "normal" weight of 190ish, but that's still a lot of meat to stop. A lot of my riding is in NW Arkansas, so a decent amount of descending. I had only really been considering matching brake calipers to whatever shifter I was going to get. Those Hopes look super interesting, though. If they work for you at 230lbs, that's a good reassurance. I'm sure your descents are a lot longer than mine.