I'm rather impressed with the performance of the dune lizard. it has a pretty good armor class and piercing attack rating... at lev 18 my Dune Lizard is holding his own quite well even up against a lev 30 Dragon Lich... Efficient tank pet in my opinion.
It's been proven that all three of those pets are exactly the same except in the damage type they deal and cosmetics. Warthogs deal Blunt, Bears deal Slashing, and Lizards deal Piercing (if I remember correctly).