Depends on your playstyle! And if you care about meta or not.
Ive played all tanks, but only dh, bdk, warr, pala and brew to 3k+ io in this expansion. Ill give you a little bit of my own personal input here:
Brewmaster: very finnicky, does have some aggro issues but once you get comfy rotational wise i didnt feel like it was too much of a problem. Managing your stagger correctly is probably the hardest. And youre most likely not gonna do as big pulls as the other tanks (in higher keys)
Paladin: very cd dependant, has okay selfsustain. Interrupt king, very nice to have if youre gonna pug and a bunch of utility aswell. I can imagine there will be mana issues with some of the healing checks in dungeons. Did i mention the interrupting shields?
Warrior: pretty beefy with just your active mitigation. Albeit very prone dying to dots and magic damage. I feel like warrior is pretty fun to play, since it just looks awesome going into avatar and just smashing everything. Almost no selfsustain.
Bdk: one of the tanks i enjoy this season. Playing sanlayn can really pump some good dps, doing upwards 2.7 mill dps overall in certain dungeons. Obviously is the king of selfsustain. Has a lot of tech using ams. Grip is pretty handy (think archers in priory). You do need to know how much damage you can take especially if you do higher keys. Otherwise you just fall over. Also if you dont have ressources banked up (bs, rp) then it can be pretty nervewrecking. Otherwise its just smooth sailing, an immortal god just walking around.
Vdh: almost as high selfsustain as bdk if youre playing aldrachi. Pretty beefy with just spikes and parry from sigils and your aldrachi buff up. Has really nice utility, especially when paired with boomie (chains into beam into silence sigil) makes some pulls a walk in the park (workshop first pull). And obviously youre a demon, thats pretty nice. Can be a problem hanging onto threat, since a lot of the abilities are bugged.
Sorry for the many short sentences. But im on my phone 
Edit: also if you plan on pugging in the 12-13+ range, expect the meta mentality to kick in. So if youre not playing vdh you might get some declines. Although is never as bad as the dps queue simulator game!