Without a shadow of a doubt, The Simpson's has had an incredible run, and many episodes are full of classics. However, it is a (very) aged show that has run it's course.
Family Guy on the other hand, well, just appeals a lot more to me since it has a lot more edge than The Simpsons. The Simpson's makes (horrid) spoofs of certain pop culture events/people by creating a totally fictional yet obviously inspired character to take the fall. Family Guy on the other hand doesn't seem to have a problem getting an actual celebrity in to make fun of.
That and Family Guy has the sheer randomness factor. I hate it when I hear Family Guy called a complete ripoff of The Simpsons since, God forbid, you can NEVER have a family that happens to have an infant and two older children, one male, one female, and a dog. Nope, we can't have that, can we?
People just get so anal about the fact that a TV show has a similar setting/premise as something else. Star Trek, Babylon 5, Battlestar Galactica...what do these all have in common? Hmmm Let's not forget that The Flintstone's was basically an animated stone-age version of The Honeymooners.
So, that little rant aside, I prefer Family Guy. The Simpsons is just too dry for me, and I have no problem at all skipping the show.