Tanking while leveling: Who's best?

So in my continuing journey to learn how to heal, I am pugging a lot of groups. And a trend that I am seeing is that the only tank class being leveled is the Death knight. Last night, while attempting to run Blood Furnace with my mage, I had a discussion about the best and worst tanks while leveling. As a benchmark, I consider leveling pre-78. After 78, you're running 80 instances and gearing up for heroics and gear starts resembling a lot more what you'll have in endgame. That being said, I believe death knights to be the worst tanks in the leveling phase of the game.

All things being equal (player ability, experience etc) tanking comes down to three things: Threat, Health, and mitigation. Threat because you want the mobs beating on your tough armored ass and not the puny guy with the creepy laugh standing in the back in his sissy robe (lol). You want health because once they start beating on you, even with heals, you need a buffer to stay up, more is better. Mitigation is important because even with a ton of health, you don't want every attack to hit you, you'll drive your healer nuts (TRUST ME!!)

This is how I feel the classes stack up (fairly subjective, although I have one of each, theyre not all the same level and not all geared/speccd for tanking)

Threat: Paladin, Warrior, Druid, DK. Paladins generate the most AoE threat the easiest in the game. They are threat machines. If you have a pally tank and he can't hold aggro, something is wrong. Warriors have a lot of tools for individual threat, and their AoE threat has improved a lot between end of TBC and wrath. Druid threat is based mostly on damage, but they do have Berserk to do massive threat to up to 3 targets or get a sizable jump on boss fights, still when I have tanked on my druid, threat has been an issue. Lastly, Mr DK. Their threat is based mostly on damage, they only really have one AoE threat generator: Death and decay(which they don't get till level 60), and don't get a taunt until 65. Death grip is not a taunt boys and girls. As they don't have a tanking spec they are more a hodge podge of abilities.

Health: Druid, Warrior, Paladin, Death Knight. My druid at level 70 in dire bear form has around 14k health. At the end up TBC, I struggled to get to 11k. My warrior has around 11k HP and he is neither prot nor even level 70 yet. Again, death knights lose out here. The major factor is most tanking shields have a good amount of stamina, and a lot of death knights focus on DPS gear. With a true "tanking set" they would probably only lag behind slightly just because shield + 1h weapon generally gives more stamina than a 2h weapon.

Mitigation: Paladin, Warrior, Death knight, Druid. Again, shield is the biggy. Paladin and warrior are probably interchangeable here. Paladins will have higher block, but block isn't as useful a mitigation stat as parry and dodge. Death knights have a higher parry and dodge, but no block at all while druids basically get dodge only.

Ghostcrawler has pretty much said they tune classes for 80. We have a death knight tank in our guild who tanks our raid runs. Obviously, there are DKs who are successful despite their lack of tools. My point is they do have a lack of tools. Another thing to consider is that a death knight is normally an alt. How many people who tank on their main roll up a tanking alt? How many people can learn to tank in 20 levels? My answer to both is probably not many.

While there is no clear answer who the best leveling tank is, it is clear that the worst leveling tank is definately the death knight.