Re: the 4th spot, I think Alabama is probably most deserving with just 1 loss, to a good Auburn team that seemed to be peaking. They rolled most everyone they played, though that opening game win vs. FSU turned out not to be so impressive, even though FSU did have their QB most of the game.
I'm not a big fan of the argument that you have to be a conference champion to get in since that ignores non-conference games, but I do like some regional diversity. Otherwise you can get caught assuming one conference is better than the rest when all they are really doing is playing each other. I'd rather see them have to prove it against other conference teams. That said, OSU lost their only tough non-conference game (to Oklahoma), and you cannot ignore that Iowa game.
So I'd go with Bama, but can see why they might take Ohio St.