Both men had their moments. Obama's tone and posture was much better. A lot of it might have to do with McCain's POW injuries, but the visual was very striking, I think, and that matters a lot to the dreaded "low-information voter".
I was really struck by how often McCain called Obama naive, or unprepared, or that he just doesn't get it. It's all well and good (though not particularly illuminating) for McCain to say that. It would have been better to demonstrate it, which I don't think he did.
All in all, I think that because of the difference in body language and tone, as well as managing to reassure voters that he can hold his own against McCain on foreign policy, will give Obama an edge coming out of this. While Obama was never particularly strong at any point, he was solid all the way through and didn't give McCain or SNL anything to parody. I think Darrell Hammond got some material for his McCain impersonation, though.