Brakes are one of those endless debates of mountain biking. Every one has an opinion and usually its wrong for you because everyone seems become fond of what they have.
That said, I have has several sets of Shimano hydraulics (Deore M525's and original Saints) and never had issues. I had a Hope Mono Mini once and it was pretty poor, but I was new to biking and it was probabbly me being a spanner more than the kit. I've has a crack with new servo-wave style XT's and they seemed properly spot-on, but it was a brief usage. I've seen elixers but never used the "in anger" so can't comment on these.
(Personally, I would recommend Avid BB7's for everything except DH.)
