I demoed a couple of bikes with XT brakes today and they are really nice, pretty grabby though but I guess you get used to that, certainly very powerful. I also rode some Hope tech evo somethings and they were also excellent, and I preferred the progressive feel of them to the XTs.
I've had a Deore on a bike for years and it is still one of my favourite brakes, great feel and good power, less grabby, had no problems with it at all, though the lever isn't as nice as my Oros or most other brakes I've tried.
Basically you can't really go wrong with either. As a piece of engineerin the Hopes are a bit more special.