I am looking to main a tank in Legion and I am the most unfamiliar with the monk class. I have never touched it. I'm curious as to how the Brewmaster spec is doing since the patch. Does it feel good to play versus prot warr or blood DK? Obviously there will be a lot of opinions in here and that's what I'm looking for.
Unless you're in a cutting edge progression guild(in which case your raid leader will be telling you which to prioritize and you wouldn't need to ask this here) it doesn't matter. All are viable. Go and play them and figure out which you like, instead of asking heavily anecdotal questions like "which feels better".
No one can tell you what you will enjoy. All tanks will be viable for all levels of content. Unless you're at the top of the top of raid guilds, playing a class that you enjoy and are good at will mean more to your abilities than the class.