Some of this info may be a bit dated but here goes:

2nd tier:
-- Best i've seen is the tuara lizard - does some damage and usually regens well enough to be a continuous tank at those ranks
-- Second best for me would probably be the wombat, dodges semi well and seems like it had one pretty decent attack a round

3rd tier:
-- Best is a close call between the sand lizard and the bobcat. They both do some damage and it depends on what kind of group you have for which is better. If it's a weak group, sand lizard is probably better because on easier mobs you can get a sustainable thing going. With a good group (especially with a bard for further resist and some healing) a bobcat can take damn near anything you need it to.
-- Next on the list is the hare. The hare dodges as well as the bobcat but i put it here because the bobcat gets some dam resistance while the hare gets forage (and danger sense i think i remember).
-- Last is the tortoise. This is the precursor to the enormous let down of the dillo. About the only way i've ever found to make a use out of the tortoise, is if you find mobs that hid hard once a round (preferably with a blunt attack) and you have a warrior to feint for you. Other than that, it's just a slow way to die.