Who wins the fight (One guy busted up but won on score cards)

That's one of the stupid misconceptions people always make. Fights are scored on a round by round basis. If the guy that's busted up won more rounds, then he won the fight. Blood means nothing.

If one fighter gets more busted up and the other barley has a scratch, the fighter that is busted up wins the fight on the cards and has better punch stats What you guys think? Does the busted up fighter win cuz of the better punch stats or does the fighter that does the bustin up to the other guy win? Its scored on round by round basis, you can't just say oh hes cut up more so he loses... if they outboxed them in the rounds and won those rounds and wins more rounds in the fight then they deserve the decision regardless of cuts. Some people cut more easily and get nose bleeds easier than others, or swell more easily... just because they bust there face up a bit doens't mean they deserve to win, if they boxed better and got the better of there opponents in the rounds enough to win enough of them to get the decision then they deserve the decision, or in the amateurs if they manage to land more clean shots. Being a little bust up is irrelevant, if you got the better of him (using whatever style) more effectively than they did you then you should get the decision, period.

Lets say the busting up happened in the final round but the "busted up" fighter won every round previously. Why would we want to think that the other guy won?

the one with the clean more effective punches... a busted up face can come from many things such as a head butt..

Boxing is not a beauty contest.