It depends on what fighting style you prefer,
Il make a quick list of the animals which share the same move set, the humber at the side is an estimated stregnth out of 10.
Rhino 8, Cow 3, Sheep 4
Wolf 8, Lion 8, Tiger 8, Leopard 8
Tutrle 3, Bear 6-7, polar Bear 6-7,
Ape 3, Chimp 2, Gorilla 8, mandrill 5
Horse 3, Zebra 3
Ogre? 5-6
CI-
Aligator- 10 :suspect
Chicken Unknown?
However you can exercise any creature to become strong. The creatures with higher strength value don't loose much strentgh compared to other creatures and are stronger to begin with.