Real gamers play pro evo (it and winning eleven are the same) but people who don't know any better and want pretty graphics and all of the teams+names play fifa. Pro evo is a much truer soccer simulation but it doesn't have the bells and whistles that fifa has.
It's kind of like Fifa is a 3.5 who spanks amazing winners once in a while, while pro evo is a solid 4.5 who is consistent but not a pusher.
The exact same situation is applicable to the hockey games, with NHL2k being equivalent to pro evo and NHL equivalent to fifa
All of that being said...fifa and nhl are still way more popular for some reason!
pro evo was the superior game a console generation ago (ps2), but in the current generation the latest PE iterations have been pretty weak. on the other hand FIFA has really improved and imo its the better game right now.
FIFA feels so robotic, I still play Pro Evo 6, although I think Konami have been making it less good since Pro Evo 5, which was the nearest thing to perfection imo.
I have both for Xbox 360 and me and my brother play Pro Evo the most. It takes more skill than Fifa and Fifa is just ridiculous with the passing, its hard as hell to complete a through pass.
However, I still find that both games lack the realism factor, in that the skilled players like Ronaldo and Pato have a rather hard time getting around a defender.