There is no doubt in my mind that Federer will be No.1 at the end of the year.
Now, objectively, I still think Nalbandian will be able to do it, wether you like it or not. Nobody ever mentions him, but I think the whole world should see his potential. To be honest, if he doesn't do it, unfortunately, it will be Federer who'll be number one. Let's hope he's not.