Originally Posted by ninjaRoller
I say take the shimano deore derailleur... unless you have a FSR-style bike like the specialized enduro, stumpjumper because the shimano derailluers hit the chain stays. The SRAM X7 won't hit it.
Hmmmm, my XT rear derailleur doesn't hit the chainstay on my Stumpjumper...in fact, it isn't even close.
Like some others have said, if cost matters (only for a few of us would it not - myself NOT included) and you already have Shimano shifters I'd go with the Shimano. Some of those that prefer SRAM may prefer the different lever style over Rapidfire. A properly adjusted derailleur, with a clean (relatively), and well-lubed drivetrain will shift great. One other variable is the cables. Old, dirty cables will shift like crap. People have their preferences, but mine are the Avid Flak Jackets - fully sealed with a great compressionless housing. I've had no problems with mud or ghost shifting.
I vote Shimano with a quality set of sealed cables.