Cleveland Show. *hides from the flames*
But really, I can't compare the two. The Simpsons, while not a family-friendly show, has always had a sort of "heart" to it. Family Guy, on the other hand, will go as far as the FCC allows them, and even then they push it just a bit farther. Completely different styles that I like for completely different reasons.
That said, if I had to choose one, it'd be The Simpsons.
"This grass feels funny. It feels like... pants." - Kirby
Also a song.