Spinosaurus vs Rex:

Spinosaurus: has two modes: one for travel and one for attack. It’s faster and stronger than the Rex depending on the mode. Four legs = faster Two legs = stronger

Rex: only has one mode but has higher health and stamina than the spinosaurus. The Rex is basically a tank that can take some hits and it may not have as good damage as the spinosaurus, but can deal a lot of damage.

They are both good. Just choose who you want