I've had both, and I prefer the shimano shifters. I like being able to upshift with my index finger, and on the new shimano stuff you can upshift with your thumb from underneath, or your index finger over the top. As for shift quality I couldn't tell a big difference between the 2, other than maybe the XO stuff downshifts just a little easier. I never tried a SRAM cassette on advice from a few of my friends that are also larger guys, they were folding the gears over. Maybe the newer SRAM cassettes don't have this problem though. XTR rear derauillers have proven pretty tough for me. A good example is this past weekend I rode at Santos, and fell over on some rocks on the Vortex trail. I didn't realize it at the time, but I broke a spoke, and twisted the cage on the derauiller. Finished off the ride, probably another 11-12 miles after the incident, and finally found the problem during the week. Put it in a vice and used some pliers and a screwdriver to pry it back straight. Good (almost) as new! My XO derauiller was pretty tough as well, but it looked pretty crappy after a couple of crashes as the carbon got goobered up pretty easy.