Don't think there's meant to be a lot in it. If you have a personal preference between shimano and sram go for that. XTR stuff does look very nice IMO.

got the full xtr kit and it runs really well, solid shifting, smooth, fab brakes. would recommend this groupset to anyone. I went for the triple but have only used the granny ring a couple of times. i also have a lot of sram kit on other bikes but prefer the xtr. this said, i have not had to upgrade any of it yet so have to think about which other parts of my body to sell to afford the replacements!

XTR probably. Much broader range of 3rd party BBs whn the original dies.

Neither. XTR is awkward to fit...the crank bolts have a habit of evaporating because of the huge tension required and the melt factor of the metal used.... and need easyout...ing. AND replacing the chain rings will cost you an absolute fortune. SRAM xx is more than likely to undo on you and cause damage, aswell as being horribly expensive to restore when it wears out.......IF YOU CAN GET SPARE PARTS...Fisher Outdoor are not very good at providing back up parts for SRAM products.

Forget about both and get something sensible