To be fair you can ping pong with both games to an extent if you want to, but I think PES makes it harder to do for a prolonged period of time. Either way, if you want to play that way it's still possible in both unfortunately.
I'm actually really interested to see what the FIFA12 demo offers, I've largely ignored the gameplay videos because I hate how people in them try and play, brings out the worst in the game to be honest. If I get this it'll be purely for the single player so I can play on my own terms, but it's gonna have to go some to get my money. It's competing with PES2012, Unchartered 3, Forza 4, Bioshock Infinite, Batman, Battlefield 3, Gears of War 3 etc so it's got a lot of work to do to convince me to part yet more cash for another game on top of those! Good times!
Agree with Calcio about PES playing it's cards already, the demo is a 'taster' to show some of the new features and is code from early this summer. Any comparisons shouldn't really be made until the second PES demo comes out. Hopefully though FIFA will quietly surprise people this year, I'd love for it to be amazing, as a football fan it'd be great if both games were equally as good as each other.