At 101 the strongest Tank by far is a Vengeance Demon Hunter. We have the highest DPS of all tanks, the highest mobility and the best self-healing. One of the reasons are the increased stats to compensate the lack of talents.
With 7.1 we will lose AoE Fear and Spell Damage Reduction which doesn't matter at all in PVE. Only in PVP it is :sadface:. But in PVP Tanks are more than squishy anyways atm. Hopefully it will change in the future.
I haven't played a DH at 101 but after seeing a friend's basic (835) geared 102 DH, I would disagree with My and say that DK's are better
For aoe dps, Blood Boil deals really good damage (64k non-crit, cd reduced by haste) and then you have Blood Plague + Death and Decay + Heart Strike cleaving 5 targets. Our artifact ability Consumption hits for ~150k (non-crit) in a frontal cone.
Our survival in aoe situations scales pretty well too:
- You can get a trait that makes Heart Strike heal you for 25% of the damage it deals
- Blood Plague heals you for the damage it deals (~115k over 24 secs) which includes the Blood Plagues applied by your Dancing Rune Weapons
- The left-most golden trait makes Vampiric Blood give you an absorb at the end for 5 times the damage dealt by all your Blood Plagues in it's duration (including the DRW ones)
- Consumption also heals us for the damage it deals
Burst dps is crazy good with the DRW traits which basically triple your DPS for 14 secs.
As for PvP, I can hold my own against most 110s
Honestly though, if all you're wanting to do is farm instances and open-world mobs, it would be a lot cheaper to make a 99 twink. You can get a good set of gear just from a day of questing and you can get all the gathering profession quests that a 101 can.