Fundamentally whomever you think it was. As much as CNN was trying to turn this into football in a way "Debate Night In America", when it comes down to there is no way to keep score. It is a bit like figure skating in that whomever you feel did the best job when it comes down to it is the winner.
You are going to have spinners and pundits all says 'He looked good', 'Got a zinger in', blah, blah, blah.
Since a debate, like any campaign activity, is all about convincing people to vote for you the winner is the guy you end up voting for.
Then again, what do I know, I am not even watching the thing.