I'm not a fan of either "Simpsons" or "Family Guy". I don't find either very funny and because of that have hardly watched them. "South Park" would be good if they cut out all the sexual content--get rid of those bad jokes/words and you have a clever show. I've seen more of "South Park" than the other two combined, but have never watched it on a regular basis--usually just when someone has the DVDs and pops one in. I'm one of these people who would much rather watch sports on TV (unless it's poker, which I just find to be really boring on TV).
I guess I'm just not that into cartoons. I never saw many at all when I was little and I didn't even know what Nickelodeon was until I was in kindergarten and other people talked about it! In fact, I didn't even see a "Bat Man" cartoon on TV until I was nine. Some of the animated/computer movies they make (such as "Finding Nemo") are quite good though.
But yes, "Simpsons" and "Family Guy" do nothing for me. I'd rather watch sports or "American Idol".