This one would be tough, but Legendary Godzilla would probably win. Not only did he get a serious power buff in King of the Monsters, but he's also several millions of years old. Shin Godzilla on the other hand is... I don't know, anywhere from a few days to a few months at best? So Legendary Godzilla clearly has more experience.



On top of that, Legendary Godzilla's Nuclear Pulse attack is the strongest that's ever been shown in the franchise, completely obliterating King Ghidorah in a mere 2-3 shots, straight up disintegrating his wings and 2 of his heads. If he goes Burning Godzilla (if he can since we don't know if he can activate it at will. Yet.) I doubt Shin Godzilla would be able to withstand them.



And honestly, judging by how Shin Godzilla seemed to be in constant pain from how he was acting, I don't think he'd be able to pull himself together to effectively fight Godzilla long enough to actually kill him.



So, yeah. I think the most likely victor would be Legendary Godzilla.