Post by Boyne
I may do the following (others may or may not agree with me, that's cool.)
Sorry to nit pick, but I just felt the need to point out one or two things. Obviously your own milage may vary, but I'll throw in my own 2 cents anyway. :P
Unholy tanking:
http://www.wowhead.com/?talent=j0xZ0xZcxGhxbogeqRcohtYou really do NOT want to give up Scourge Strike. Not for anything. It's one of the hardest hitting skills in the game for DKs, and makes Obliterate (which will consume your precious, lovely diseases) obsolete.
Also you really should get Rune Tap and Bladed Armor. BA increases your AP; more AP = more damage (and spell damage) = more threat. Odds are your gear will be low on AP, but high armor, so Bladed Armor may almost be essential for any tanking build.
I wouldn't get Master of Ghouls myself. Having to deal with micro managing your pet while tanking is a recipe for disaster. You'll have enough things to worry about without adding one more to the list.
I would also recommend Wandering Plague as it's likely to be useful on multi-mob fights.
And finally, although I know I probably sound like a broken record by now, Necrosis sucks. Seriously. Impurity didn't thrill me, but with Bladed Armor and much better gear, it could be more valuable. But I can't see Necrosis ever getting better unless they change it again.
http://www.wowhead.com/?talent=j0E0oZ0xZcgGh0bkge0ocsutWould be my recommendation. But again, ymmv.
Frost tanking:
http://www.wowhead.com/?talent=jbEZhxxtccbRMRAsot0xMy only criticism here is Blood of the North. It's not a bad talent, but I think I'd rather have Rune Tap, Rime and Death Chill than this one talent.
Blood tanking:
http://www.wowhead.com/?talent=jbEGoIIcof0tuVo0xxzZ0xPersonally I'd get Unholy Command over Butchery. Butchery isn't going to be much use to a Blood DK tank. You just don't have a lot of things to spend those RP on. (It's not like a warrior who's gimped without rage.)
Also Vendetta is a complete waste of talent points. You're rarely going to land the killing blow on a target, and even if you do, at that point what difference does it make if you get a measly 6% health back. Your healer will heal you for more than that DURING the fight, which is when it will actually matter.
I'm also unimpressed with Scent of Blood, and I'd much rather have Subversion instead.
http://www.wowhead.com/?talent=jcEMoIhIof0tuVo0xxzZ0xMIs what I would use.
If you really wanted to go crazy theoretically it looks like you could just about do a hybrid between the three, but you'll probably be doing that at the risk of losing talents later in the tree that could prove to be invaluable. So do crazy hybrids at your own risk.
I would NOT recommend a hybrid. Now that the 10th tier talents give expertise, you do NOT want to lose that. I don't know how hard expertise is to get at 80, but at level 80, 5 expertise = 47 Expertise Rating. That's a lot of itemization to give up.
But in the end, I think you can make any of the DK trees work as a tank.