Megalodon was slightly larger, heavier, stronger and faster over short distances, but had poor maneuverability when swimming up and down, in addition to a sensitive abdomen due to being a shark, meanwhile, Leviathan had a hard head and greater resistance due to his hot blood, although he had the disadvantage of not being able to breathe underwater; Its great intelligence would allow it to develop a strategy of tiring the megalodon and attacking it from top to bottom on its dorsal fin, then headbutting it in the abdomen and it would win. Let's keep in mind that Leviathan was like a gigantic mix between a sperm whale and an orca, while Megalodon was like a giant white shark, and both the orca and the sperm whale easily win fights against white sharks, For me levi wins!