When you are comparing default installed versions of Fifa 10 and Fifa 11 (PC versions), Fifa 11 is light years ahead (no doubt).
But that does not mean Fifa 11 is the ultimate soccer gaming experience on PC. Yes, graphics are better, animations are better, default gameplay is better, many many things are better. The difference is not THAT HUGE when u compare a properly modded Fifa 10 and the current Fifa 11. After applying Duong's graphics and RegularCat/Onsche's ai files and emotion files, Fifa 10 was very enjoyable ( for some). Add to that the moddability in terms of stadium adding, face modification, roster modification etc, the great tools like CM10 FM10 etc.
Fifa 11 is being worked on by the modders for about a month or more, but it is still not clear whether Fifa 11 will be even 50% as moddable as Fifa 10 was.
Surely there are many major glitches in Fifa 11, which needs to be sorted out immediately (like lagging problem for many users, Manager mode problems, weird generic faces to name a few), but if the game is not moddable as Fifa 10 was, I cannot say there is a difference of light years (or day and night) between a default Fifa 11 and a properly modded Fifa 10. Default engine of FIFA 10 was bad, but it was an evolution process starting from FIFA 06, and so modding tools were all the similar since 06 version. As days went, new things were "discovered" for modding different stuffs in FIFA 06-10. So it was possible to scale a bad game like FIFA 10 to something playable and enjoyable. If I am not wrong, the maximum number of mods that were released for any FIFA installment was during FIFA 10 (coz of maturity of editing tools and knowledge of the modders).
Now the situation is different. We really do not know whether modders can edit the gameplay AI,the teams, players, tournaments, seasons etc, what is the limit of the number of leagues/teams/players in the game, whether they can add commentaries and chants, whether the annoying errors can really be fixed (like many Manager mode blunders, scoreboard fixes, weather effects etc). We do not even know if any editing of some part will hamper other parts of the game (i.e. leading to a new "bug").
To gain the maturity level of modding that was reached in the previous generation of FIFA series will require some time, and that may even cross 1 year (i.e. the next installment of FIFA and PES may come up).
Manager mode is similar to FIFA MANAGER game but with a lot of small bugs.
So... conclusion is play PES 6 with new Shollym or PES7 patches.
No really, FIFA 11 is waste of time and PES11 have some very good gameplay improvements but with lot of bugs that will may or may not be fix with patches.
P.S. : I am discussing about PC versions only!