and have their strong points. My preference is for the Shimano system. IMHO easier to set up and maintain and the bearings are better sealed and last longer.
But I've got friends that use the RF system an they are happy with them as well. But most have replaced the bearings at least once in the last couple of years. My LX HTll cranks are still on their original set. But if you ride the RF bearings till they crap out and then replace them with Enduros they last about as long as the Shimmy bearings.
I'd second that opinion. If your riding environment is wet and muddy the Shimano bearings will likely last longer. If you were going with the RF cranks I'd lean towards installing a set of Enduro BB Bearings right from the start.
It's too bad that the new XT cranks don't have the same slick preload adjust system that the XTR cranks have.