I'll give the victory to Sin because he can not die as easily as Godzilla can, also Godzilla is only a main threat to the modern-world Tokyo Sin is the worse threat ever in a magical world (and not just one country in particular). That's got to count for something.
godzilla would win cause he looks more badass then sin xD and sin looks a piece of godillas poo xD!!! ok back to discussion godzilla can breath atomic fire at sin and actually fight sin hand to han even use his tail :P but i dont know much about sin so im going to research :P