With my 4 hunters I have 2 scorpids, a crab, and a turtle.

The turtle is an excellent tank, especially since he has a shield wall like ability with a very short cooldown. It decreases dmg done to him by 50% for like 8 seconds or something. Has saved his ass quite abit.

Since he's a turtle he only has bite, growl, and the shield ability. A bear can have claw and bite, so you get a bit more dps. So go with either a turtle or bear.