The best morphs are:

Tiger (very strong)
Lion (a bit weaker than the tiger)
Cheetah (good at dodging)
Elephant(strong punch attack)
Wolf (good against the lion but weak to kangaroo)
Hippo (like the elephant but can swim)
Orca (like the hippo)
Seagull (weak but can fly and dodge well)

The dog, chimpanzee, baboon and kangaroo aren't as strong but are
still quite good.