Warrior is the funniest when it comes to tanking bosses.
For spamming heroics, a paladin is the best choice. Pure faceroll, with only mana as a concern.
DKs are actually quite hard to tank as, runes on cooldown combined with retarded, ninjapulling DPS will be a real challenge. Though, if you go as blood, you have zero downtime outside of dungeons. Pure faceroll there.
Druids, well, as said, SWIPESWIPESWIPE.