Gladiator or Marauder. They're both tanks, but trust me on this. Tanking is dead easy, just use AoE enmity abilities as many times as there are mobs in the pull (so, 3 mobs means 3 overpowers/flashes), then use your enmity combo. Mark monsters to try and direct DPS to focus on one target if you're feeling lucky (a lot of DPS are blind). That's about it for tanking.

The plus side is that on the vast majority of bosses you just tank and spank. A lot of boss moves can target anyone BUT the tank, and you generally don't have many special mechanics to deal with.