Just to add a few comments that haven’t been mentioned yet for anyone looking for more opinions (loads around the web already though!)…
First, I would say both are very good.
I would say that shifting from SRAM is quicker and smoother than my previous XTR…. in the dry
My main gripe with SRAM is that the rear mech doesn’t seem to perform that well in the mud- the jockey wheels seem to get clogged pretty easily which in turn makes shifting a little imprecise and the chain doesn’t always settle in the correct gear.
Aftermarket spares and bling upgrades are also more readily available for Shimano.
As far as cassettes go I would say get a 12-28 Ultegra (or Dura-Ace if you are flash) and save tons of weight and money on the MTB equivalents. Durability has not been a problem at all for me over the winter, and the closer ratios are a real plus.
Finally, I don’t know why anyone would go for Hope’s XC brakes when there are so many better options on offer. I personally went for R1’s and have been blown away with the performance. The new XTR brakes seems to get good reviews too.
It’s nice to be in a position to worry about XTR or X0 😉