I'm not talking about which game is easier, or more fun or any of that when I'm suggesting it's more of a simulation but rather in how it emulates the sport. For example; each individual player has what are called attributes and unlike FIFA they actually make a tangible difference in more ways than one. Now that isn't to say it's a pure simulation as I believe (and some PES fans will contest this) that the game cheats in many respects to make the difficulty harder (artificially lowering your own players attributes or ignoring them in some cases if you like).
For me FIFA is all gloss... except somewhere along the line (right after the release of FIFA 97 and starting with FIFA 2002) EA Sports decided that their games no longer needed that veneer and so they are just as turgidly boring and one dimensional as ever only now they even look it! Muddy, low resolution textures, disproportionate perspectives and models along with special next generation graphical effects such as bloom which make the game even more artistically repulsive.
I personally think the FIFA franchise benefits from the apathy some people feel towards Football Manager and Pro Evolution Soccer. The latter titles simply aren't improving enough to make the difference between versions as satisfying. So then they play a game that's been neglected for so long and nostalgia and the fresh feeling it provides accentuates their experience.
Either way PES and FM shits all over the opposition. Although it's a shame that there's not enough real, genuine competition.