To be fair I really only have experience with DK/DH at 101 so far. I actually think DH will pull ahead of DK once I can get mine at the same Gear level, ~800 iLvL. At 758 my DH already pushes about the same DPS as my 801 DK but takes quite a bit more damage. My DK on the other hand takes almost no damage at all but can't Heal back up as fast as my DH can.Blood DKs are the least equipment gated. Prot pallies and Guardian druids if you manage to get the M-HFC trinket would be my two choices if I could have any gear I want.
DH will pull ahead of DK
If you're properly Gearing your 101, you should have 20% Avoidance (requires ~560 Avoidance, or an iLvL 855+ Helm/Chest) and the rest full Leech. Speed is fine when you need the movement, say WPvP and certainly clearing old Raids, but for PvE (WoD Raids+) Speed is of little importance so it should be pure Leech after the 20% Hard Cap for Avoidance has been reached.On a side note has anyone played brewmaster? Even with near full time uptime on ironskin brew they seem pretty lack lustre unless you have tons of leech pieces... Any clue on how their dps is?
If you're properly Gearing your 101, you should have 20% Avoidance (requires ~560 Avoidance, or an iLvL 855+ Helm/Chest) and the rest full Leech. Speed is fine when you need the movement, say WPvP and certainly clearing old Raids, but for PvE (WoD Raids+) Speed is of little importance so it should be pure Leech after the 20% Hard Cap for Avoidance has been reached.
Once everyone starts obtaining several 890+ pcs, we should all be 20% Avoidance, ~22% Leech (ALL World Epics + HFC pcs with Leech) and whatever Secondary setup is best for your Class/Spec.
My reasoning for saying that you should cap Avoidance then go pure Leech (for Mythic HFC > Legion PvE Content, except soloing Dungeons) is because with a single piece of Armor, 855+, you can hard cap the value at 20%. No other Tertiary Stat can give you that high of a value from a single item, therefore it carries a much higher Itemization value. Is it 'needed' on well geared 101's, probably not, but you're only losing 3.5-7% Leech/Speed if you chose not to take Avoidance and it gives you the option to basically stand in stupid instead of having to move out of it, mostly.Avoidance is nice to have if it just happens to be on your gear but I didn't think highly of it as a tank. AoE damage is usually intended to be survived by the entire raid with the exception of frontal cones, so as a tank it's often trivial. Maybe the explosions on Xhul and orb damage on Iskar but most bosses were only difficult to survive because of stacking debuffs.
You'll appreciate speed a lot more if you ever try soloing Tectus mythic, when you're surrounded by 4 Earthen Pillars and moving a fraction of a second too late gets you insta-killed
Leech is by far king of the stats though and I slightly regret not finding a full set of it. I might even rate it higher than all the other secondary stats - pretty sure we can get over 50% at a decent ilvl which is a lot of healing with the DPS we do at 101.