pvlbpc :
what the best?
GTX 1080 Ti ASUS Rog Poseidon
GTX 1080 Ti Gigabyte Xtreme Edition
GTX 1080 Ti EVGA ICx Elite
Whichever one you get your hands on.
No seriously, the differences can't be that much as they are all premium models. So I'd say whichever one you like the most is the best one for you.