I put Leopard, although I have never had to shoot one charging. They may not do as much damage but are fast and small. Sneaky little Bastards too.

Lion second, smaller, fast target. If you see them first you can anticipate the charge and shoot before it gets going.

Elephant third, So big for a CNS shot

Buffalo, fast and tough, small target areas but can be turned

Rhino, big, slow and easily maneuvered around