Crocodiles (& their relatives, alligators) are generally viewed as top predators. They're 'ambush' hunters1, lunging up out of the water to snatch at their prey at the last moment.
But sometimes, they come off second-best. Check out this video on the National Geographic site, of a jaguar stalking, catching, & killing a caiman.
1 Having said that, when I was writing this post I came across the intriguing suggestion that some crocodilians use sticks to lure birds within lunging distance ie that they use tools. They've been observed doing this only during the birds' breeding season, when their feathery cousins2 are looking around for sticks to use in nest-building.
2 Taxonomically speaking, crocs and birds are both archosaurs. Early crocodilians – the pseudosuchians – were a predatory force to be reckoned with & it's possible that the pseudosuchians' demise, in the mass extinction that marked the end of the Triassic, was a factor that opened things up for the expansion of the dinosaur lineages.