Well, Obama, but not in a knockout or anything. All he had to do was keep his cool. He did. McCain had to get Obama by the throat and strangle him (metaphorically speaking, of course). He didn't.
One of the Fox analysts (I think it was either Bill Kristol or Fred Barnes from The Weekly Standard) pretty much nailed it: It looked like a tennis match with McCain running all over the court to whack at the ball while Obama just kind of stood at the baseline and nailed it every time, no biggie. It's not that McCain had a lot of misses, it's that he had to work so hard to do what came off as easy for Obama. Obama looked and acted more ... presidential.
McCain kept looping back to the already shopworn Joe the Plumber schtick. He might have been better off riffing on his one real zinger: "I'm not George Bush. If you wanted to run against him, you should have run four years ago." But he wasn't able to press that one home, and Obama pinned the Bush tail right back on him with ease.
The Ayers thing was anticlimactic. McCain didn't manage to attach any sense of urgency to it, and Obama easily torpedoed it with cool and calm rather than with my suggested impassioned retort.
A real smaller-government candidate might have been able to land some blows on Obama, but McCain isn't a real smaller-government candidate and he doesn't convincingly play one on TV. His "maverick" streak goes more in the McCain-Feingold, McCain-Lieberman, etc. direction.
On the subject of VPs: Both of them agreed that Biden is a pretty well-qualified candidate. Both of them (Obama presumably to be polite when it cost him nothing to do so, McCain presumably because he didn't want to get laughed off the stage) smoothed right past the same question on Palin.
McCain is just outclassed. It's not that his policy positions or attitudes toward government are particularly better or worse than Obama's. They aren't. It's that McCain has huge handicaps (his age, his running mate, the Bush administration hanging around his neck like an albatross), while Obama is young, self-assured, and in the enviable position of running against eight years of misrule by McCain's party. I can't even imagine how much it must suck to be a Republican this year.