Croc obviously wins in water, but I think it actually would win on land as well, as the bites of the crocodile would leave behind nice big gaping wounds while the gorilla's muscle wouldn't put as much of a hurt on the crocodile as quickly.
Most likely crocodile, whether in water or out. Gorillas are strong indeed, but generally speaking they are not as nearly as aggressive as a crocodile. Croc's are born to kill, whereas gorillas use violence only to defend themselves. They're mostly a peaceful and gentle species. A croc would latch onto a gorilla's arm or leg, and sure the gorilla could attempt to fend it off but there are few animals powerful enough to get out of the grips of a croc's jaw. The croc would do his roll, and attempt to snap the gorilla's leg. And forget about the fight being taken into the water. The gorilla definitely wouldn't stand a chance. And chances where there's a croc, there's water. And the croc knows well enough to take the fight to the water where it has the advantage. Overall, the croc would win.
Crocodiles destroy gorillas in water, and beat them by a fair margin on land too. Gorillas have superior mobility, but are pretty much limited to charging, grabbing and ripping, which wouldn't be all too effective against an opponent with teeth that could disable them with one well-placed chomp-and-tear.