I have the RC 2in on mine (2014 GMC). I never have noticed any difference in ride quality since I got it. MPG's were effected but it was a very negligible amount and probably unnoticable to anybody that doesn't keep a weekly track of it. As far as which one is the best, I have no idea. But if its any help, my dealership only would do Rough Country and Readylift. As for height, I would get a 2in, I think others will agree with me. Going above 2in is said to put stress on suspension angles and wear ball joints more quickly. That being said, 2.25 or 2.5 probably is not going to be very hard on your truck. I still went with 2in to be safe, and I think it looks great. Plus, on mine anyway, it leaves the slightest amount of rake so when you pull a trailer it doesn't make it look like its running uphill. If you want more in depth information read the post about Lift kits on the top of the suspension page.
Disclaimer: I am not an expert and anything I saw from here on out is personal experience or something I learned here.

 

I have run Suspension Maxx leveling kits on my 2009, 2013 and now my 2015 Silverado. I have had zero issues and put several thousands of miles on it. For my tastes / likes I am running LT285/65R18 tires. Just a bit larger than the factory 265s but no issues with rub even at full lock.
Good luck deciding, here is a link to the kit I used
https://www.suspensionmaxx.com/store/product/SMX-GM725

The main reason I ended up using Suspension Maxx was my tire shop (Belle Tire) installs them and both are Michigan based companies...keeping as much of my $s supporting my neighbors when possible.

 

My post here may help you out:
2.5 RC level kit install - 2014 GMC Sierra

My recommendation is go 2.5 and install the rear block. As far as kit mfg, I think you will be OK with any you choose, but RC has a lot of kits out there and few complaints. We're talking blocks under the strut and above the coils....not a lot of engineering involved with designing the kit.

As far as ride, everyday ride is about the same after the kit, but hit a speedbump or pot hole and it's a lot more jarring. So avoid hitting them! Also, stay with a P metric tire over an LT to keep your ride smooth. Smaller rim = more tire = better ride.

A 285/60r18 comes in P in a many tire mfgs, while the 285/65r18 is gonna be an LT. The P won't stand up as tall as the LT when the weight of the truck is on it but will give you a better ride.

If you carry anything in bed or tow, your truck is going to sag, look like crap, and point your headlights to the sky. I fixed that with Firestone RideRite Air Bags. I can't say enough good things about them.

 

I just installed the pro comp adjustible shocks with a 1/4" spacer. Very happy. Have about $220 in the setup

 

Thanks guys for the info. I went through all 200+ pages on the leveling kit thread and learned a lot.

Soon I will be going with a 2" RC level kit and 275/60/20 Mickey Thompson STZ. I had the ATZ on my last truck and they were awesome! I travel to and from work on the hwy, so can't go as big as I had before; and MPGs are more important now with a family of 4

Thanks Again!

 

I have the same pickup you do. '14 Sierra SLE Z71 4x4 CC 5.3L.

I studied this forum for several hours before choosing the RC 2.5" Lift and 275/70/18s.

After installing it.....it doesn't take much to get the bed to squat. A fully loaded toolbox and spare tire puts it level. Anything over that and it starts to squat.

My new Air Lift Load Lifter Ultimate air bag kit just arrived yesterday. I hope to install it this weekend.....then no more squat.