I'm really impressed by the FIFA 10 demo and so far have wanted to play it more than the PES demo. FIFA 10 feels so fluid and the animations are fantastic, even if PES may have a bit nicer player models now.
This goal I scored with Juventus really showed some of the amazing things that I am finding with the demo - using Del Piero, I saw Camorenesi making a run along the top sideline. I was able to hit him with a beautiful long ball (B button) which would never be possible in PES. I love the speed of the cross-field balls in FIFA 10.