It really depends on what characteristics you are after, and the pricepoint you are aiming for.
The range from Shimano is the best choice if you want a set of brakes that you want to just set up and forget, not having to worry too much about maintenance. I have found that I don't have to rebleed them due to performance loss, only as a maintenance cycle issue. Add to the fact that the Mineral Oil is safer to work with than DOT fluid.
Shimano Saints:-
Pro's: Very powerful, and no brake fade experienced in long subalpine descents. Lever ergonomics are nice.
Con's: Can be noisy at times. No modulation when comparing to offerings from Avid. Contact point adjustment does not work.
Shimano XT:-
Pro's: Good value, and great performance. A riding buddy uses the XT's on his Whistler rig, and can't fault them.
Con's: No modulation compared to Avids.
Shimano XTR:
Pro's: Offers best modulation out of the Shimano range. Bling, if that's your thing.
Con's: Pricey.
The other thing to consider is that if you damage your brakes, Shimano's will be easier to get replacement parts for wherever you go. However, levers are not interchangeable.
I used the Codes for two years, and:
Pro's: Powerful set of brakes, no brake fade experienced. Excellent modulation. Contact point adjustment is brilliant. Replacement pads well priced. Levers interchangeable.
Con's: Found I've had to rebleed every 2-3 months to keep getting good performance out of them. DOT fluid damages paint.
I've personally gone for the Shimano option on all my bikes, as I value the "set and forget" mentality quite highly. For the tracks we have here in Oz, a 2 pot caliper is more than ample, especially if you're going to be using 8 inch rotors on your rig.