All things equal, the stronger will win, sure. When is everything going to be equal? Even if the attributes of both fighters are level, there's the probability of someone screwing up. Everyone makes mistakes, and even if everything about the fighters was equal, save 40 lbs. on one guy, that bigger guy could still go to take a step forward and land the ball of his foot wrong, causing him to lose but a second, and that could end it there.
Too many variables to determine, really. It's all a game of chance, provided some level of skill is involved, in any fight.
That all being said, I'd say skill would ultimately be more important. There are more small, skilled fighters taking out bigger people, than there are big, bulky, biker-esque guys who get enraged in bars taking out those same small, skilled fighters...ya' know?