It's not that I think warriors or paladins are terrible tanks, they have their place and they can do some jobs very well. However, for general purpose, Swiss Army tanking (such as one finds in almost every instance), I'd choose a druid.
For a start, the druid ability Swipe is much more powerful and versatile than Cleave. Swipe is also better, in my opinion, than Consecration, which I never found held threat off of me well enough while I was spam healing the paladin.
Now, I know I am opening myself up to accusations that I've 'never met a good pala/warrior tank', but is that really likely? Is it honestly possible that I ran instances and healed for months and months, meeting druid tank after druid tank that could keep the agro off of me in almost all situations, and never once met a 'good' paladin or warrior tank? Really? I'll save you the effort, no it's not. I met good paladin and warrior tanks. They just weren't as good as the worst of the druid tanks I met.
"But LFM," I hear you cry, "you are just biased because you are a druid tank!" It could be the case. However, I was answering that question long before Ghosthoof was even a twinkle in my eye. In the argument about this particular chicken and egg, the preference for healing druids came first and the creation and leveling of a druid tank came a shockingly distant second.
I hope that has put to rest some of the initial cries of outrage.
I'd like you to know that my definition of a good tank requires the fulfillment of three criteria:
- Can take the hits the instance dishes out
- Can keep the mobs from hitting me
- Gives me an easy time healing
On all three criteria the druid class reigns supreme. I know points one and three might appear to be the same thing, but point three is more to do with attitude and competence. If the tank constantly pulls the mobs around corners so I can't see them to heal, requiring me to constantly move around to get position, then they fail at point three, while probably being able to succeed on point one.
So there you have it, part of the dual reason that Ghosthoof exists.