If you're a true football fan, you should get FIFA. It has the best depth, manager and be a pro modes, best content with official clubs and leagues and cups, and more importantly, best gameplay. You can build up the play, do different kind of passes and shoots, the AI is better and you just feel like playing football. But mind you that it's not an easy game for those who don't understand football, you must take time to learn the controls and the game. If you just want to dribble and score stupid goals from time to time, get Real Soccer. In short: hardcore = FIFA casual = Real Soccer
I tried one or the other (can't remember) on my friends iPhone, didn't really like it. Goals! on the other hand is amazing. I have spent so many Psych classes playing that. Soccer isn't really my sport, so maybe that's why I find the casual game Goals! so much fun.