I have a Deore Shadow (not XT) on one bike and I like it a lot, very crisp shifting and no cable loop. Other than that I've been using regular Deore parts for many years and had very little issues. Even if something breaks or wears out it's easier to replace a $60 RD than a $200 one. The only exception is the latest XT front derailleur: angled adjustments screws, makes it very easy to work with it.

However, I've been hearing lots of good stuff about SRAM and my next full build may as well be based on SRAM. I'd like to try Matchmakers with Avid hydraulic brakes.