This site in general is (in most cases) unreasonably anti-FIFA. Right now there is NO footie-sim installed in my PC, but if I owned a next-gen console, I'd be playing FIFA 08 right now. And I've been a PES fan since the PS One days!
PES won't "always be better than FIFA" even if it stinks. That's not a valid or even intelligent argument, and probably is the kind of mentality on the part of the developers that brought PES to being what it is today, ie. a substandard, below-par game. Play a bit of FIFA online then try playing online on PES. Play a little Gears of War and then look at the graphics on our beloved franchise. Watch a real football match and then pay attention to the rhythm of PES. Observe how real-life players behave when marking and applying pressure and then watch the robotic precision and untiring sprinting of the players in PES. See what I mean?
Goldbergio: Just so that you know where you stand, everything in FIFA is fuller and better than in PES, but the game play is not "there" yet. Of course, PES 2008 is most definitely no longer "there", so I guess FIFA wins hands down. I even like the flow of the game better in the latter, which is quite a sad fact for me as a PES fan. The 'fun' factor is probably still on PES side, but FIFA gives you more of that oozy feeling in your stomach when you make a realistic play instead of rushing about the pitch like crazy. And you can even play online decently.
An interesting parallelism: I had more 'fun' playing FIFA 2000 for a game or two, but when I wanted a real football match I turned on my PS One and played Winning Eleven for hours. PES 2008 is 'fun', specially with friends, but I can't be arsed to play it in single player. As I've said once in here, I uninstalled it after getting an aggregate victory of over 20 goals (I think it was 24, can't quite remember) in Top Player, against some top team and with 'good' (not excellent or superstar) players. Sure, it was fun, but I'm not touching the game again.
EDIT: I've just realized I'm talking 'next-gen' PES and next-gen FIFA here and you're not. If you're planning to get FIFA 08 for the PS2 or PC (ie, the 'not next-gen' version), then don't. It sucks.