White bears and brown bears have the most health and dmg, currently.
Terror Birds are the fastest tamable pets and I believe their speed was increased in the latest patch.
In terms of health and damage the campodon is way better than bears, though the campodon moves at a snails pace. I'd say the bears are great all-rounder pets for sure. Decently quick, decently tanky, pretty good damage.
I haven't had a terrorbird so I don't know how strong they are, but a direwolf is also a pretty good pet. Decent damage, can keep up with a horses trot easily, but it won't win any awards in the tankiness department.