With due respect to PiT, I'll throw in a vote for "not Baldwin"
If I had to lobby for someone, it would be Obama. I think I've laid out my reasons pretty extensively elsewhere. I think he surrounds himself with better people, and is more thoughtful. But I'll be honest: I think you're smart and informed enough to make your own decision. I don't think anything we say is going to be new information. I personally think McCain's inability to separate himself from the culture and advisers of the Bush administration is disheartening, especially for a guy with a healthy sense of honor but little curiosity. Over the past few years, I think we've had enough of "that's how it is"-ism in decision-making. Obama has a bit of that too, but overall I'm more comfortable with him at the helm.
I'm not enthused about either, but considering your ideology, I think Obama would be a better fit. But you know better than any of us. You'll regret it a lot less if you make an independent decision, even if you'll regret it either way (your damn fault for voting!). Good luck.