@OP
You'll have to define what you mean when you say "hard to take down". A mage could be hard to take down. One definition is standing in one spot using only cooldown abilities while letting a hunter unload
Another definition that might be closer to what you mean is a solo flag runner running in a straight line with a healthy mix of rogues, hunters, shammans, etc trailing behind beating on him with full dispel/purge spamming. In this case what class would last the longest? We have to assume that lifeblood, AGM, and possibly mining are constants
This is interesting because I think a Pally or Warrior would last longer than a Druid but they wouldn't make it as far.
Druids really have no CD abilites that would improve their survivability in bear form (maybe a bearform druid specced into
Thick Hide ?). HoT's can be dispelled so they are essentially worthless in the above senario. Druids currently cannot be Dranei either so I guess we can bring race into this.
Pallies have
Devotion Aura which can't be purged or dispelled and they also have LoH which is kinda like a reset button (may have to leave LOH out for this discussion). Pallies can be Dranei so Blessing of Naru would benefit them as it can't be removed.
Divine Protection although a very nice CD ability can be dispelled.
Warriors have defensive stance which is a 10% damage reduction (all damage magic and melee) this is far superior to the paladin's devotion aura and is passive. A full armored warrior should have around 2000hp with 60% physical damage reduction. This would save loads of HP in the long run and I would be interested if anyone wanted to compare this passive damage reduction to LoH in terms of effective HP. It is would probably also make other abilities like lifeblood and BoN get more "bang for the buck". Shield Block is a very good ability but is most likely useless while running away from a pack of mobs.
Shammies have slows but no good abilities to improve survivability.
In the world of WSG we all know that druids and shammies make better FC's just talking theory here.