I like the SRAM XX1 better than what Shimano is offering, here are 10 reason why:
1) Greater range, 10-42 rather than 11-40. More top and bottom end on the SRAM cassette.
2) XX1 will be about $500 cheaper on the street price.
3) XX1 has been out for over a year and is proven to work well.
4) XX1 uses X-sync which locks the chain on the chain ring eliminating the need for any kind of a chain guide.
5) XX1 is a dedicated 11-speed group, XTR tries to be both a 1x, 2x, or 3x setup.
6) I have not confirmed but it appears XTR cranks need to be removed to change the chainring(s).
7) XX1 rear derailleur path is a true horizontal parallelogram to provide quick/reliable shifting.
XX1 has a Gripshift option.
9) XX1 trigger shifter has an extremely short throw for both increasing and decreasing gear changes, provides very fast shifting.
10) XX1 cranks are offered in 2 Q-factors.