If you prefer arcade experience, then go for Real Soccer. It's easy and not complicated at all and suits casual gamers well, but can be boring for hardcore football gamers. If you want a more serious football game, go for FIFA 10. It offers a lot of content and depth. The AI is better and if you understand football, it offers much better gameplay (it's not all about dribbling and putting the ball on the back of the net). However, the learning curve is very steep and if you don't love football too much, you'd better off buying Real Soccer.
This has been brought up more than once already: http://forums.toucharcade.com/poll.php?do=showresults&pollid=707 http://forums.toucharcade.com/poll.php?do=showresults&pollid=714 http://forums.toucharcade.com/showthread.php?t=28834&highlight=football