Both are great songs and are worthy of being top 2. But I think the reason Cool won over Hung Up is that it's just so inoffensive that it's impossible to dislike, whereas Hung Up is a little more aggressive, causing some people not to like it.
But considering how bad some of these rankings were, I'm very happy with this result.
Thanks for doing this rate by the way sumthintoxic; it was fun to do and it was a great idea!