Typically, crocodiles are more aggressive than alligators, which makes crocodiles more dangerous than alligators. Alligators are opportunistic feeders, meaning that they're not likely to chase you down unless they're provoked. However, that certainly doesn't mean that you should swim with them.

Generally speaking, crocodiles are considered to be significantly more aggressive and temperamental than alligators. While both are apex predators that should be treated with extreme caution, the Nile crocodile and the Saltwater crocodile are notorious for their tendency to view humans as prey, whereas American alligators are typically more wary of humans and tend to flee unless they feel provoked, are defending a nest, or have been habituated to people through illegal feeding. The biological difference plays a role in this behavior; crocodiles have specialized glands that allow them to filter salt, enabling them to inhabit a wider range of environments, and they have evolved in much harsher, more competitive ecosystems where extreme aggression is a survival necessity. Alligators tend to be more "laid back" in their freshwater habitats, often basking for long periods and avoiding conflict when possible. However, "less aggressive" does not mean harmless; an alligator is still an incredibly powerful predator capable of lethal force, but in a direct comparison of disposition, the crocodile is almost always the more volatile and dangerous of the two species.