I'm on FIFA as well. I think I switched from Winning Eleven in 2008 or thereabouts. PES has gotten bad, but the improvements this year look like it's trying to step up a bit. But FIFA simply has the better gameplay and a tonne more licensed teams/leagues. I can't play 12 in French though and that's my biggest gripe.
I like Fifa, played also PES, but the missing licenses for PES and playing with players which have nothing in common with the reality isn't any good for me. FIFA 12 is the next fifa i played after FIFA 10. The 11 one i skipped over it.