These are both deadly predators, but I think I have to go with the Great White shark. This is only if they are fighting in deep water. The crocodile would probably make an easy meal of a shark in shallow water, but if they were fighting over deeper water the shark would be able to survive the initial attack. See the crocodile likes to clamp on and give that death roll, but if they started dropping into deeper water the crocodile would have to let go and get some air. I think on the way up the shark would probably deliver a nasty bite that would kill the crocodile.