I'm going to try the FIFA demo when it comes out too. A lot of what I'm reading sounds really good.
The reason why I'm leaning towards PES right now is that I really like how all the teams play and feel different. Every game is different and the stars really stand-out in what they can do.
I also like that they have the Champion's League.

With FIFA, I've read too many times that the teams and players all play the same.
(I guess the same could be said for all EA games).

But I really like how well FIFA does things off the pitch.