There isn’t much difference between todays groups anymore. All come with 2-way release, detachable gear indicator and you can shift more than one gear at once as well. A lot of bikers say, the haptics of XT is better than the one of Deore or SLX, because the way you have to push the trigger is shorter. Maybe there is a difference in weight or durability between the groups.
For myself, I’m happy with XT and XTR is just overpriced IMO.