Family guy is frigging funny, as is Drawn Together. I wouldn't even call Simpsons or Futurama adult cartoon, but they're great as well.
South Park takes first place effortlessly though, in my opinion.
I guess I feel the same way about it as Eric Cartman - "I am NOTHING like Family Guy! When I make jokes, they are inherent to a story! Deep, situational and emotional jokes based on what is relevant and has a POINT! Not just one interchangeable joke after another!" (Also see American Dad, which I'm surprised isn't in the list).
That may be exaggerating slightly, but the point is, Family Guy... I don't know, I think it takes the easy way out. It just gets a string of quick laughs. South Park humor is better. It stays with you.
I'm not sure how to say it.