819's are the business, and you can build them on any hub. Been using a set of 819's or another for about 7 years now. I like my Stans rims too, but 819's really are just the easiest way to go tubeless for sure, and they're damned stiff.
XT wheels look very nice, but the M775 freehub is notoriously weak and expensive to replace. Also as many will argue, the cup and cone bearing system is not so forgiving of a lack of maintenance as cartridge bearing hubs, you can't replace just the bearings in them if they get too worn! And 24 spoke only for XT, which is OK for skinny types riding XC but 32 spokes is better for about 95% of us out there...
The Bontrager wheels... Not heard bad things, but then not heard much at all! I'd worry though as just about every Bonty wheel I've ever seen has been 28 spoke, which means a right PITA if you ever need to replace a rim/spoke/hub etc...
I'm still all in favour of "normal" handbuilt wheels with 32 spokes and readily available spares. Wheelsets such as Bonty's, XT's or even Mavic Crossmax may look nice, but I know I can get a replacement rim or a spoke for my 32 hole wheels pretty much anywhere anytime... Same can't be said of most wheelsets!