I personally think south park shits all over family guy.
Family guy is just to random for it to make sense and to be funny. The jokes family guy pulls are sometimes quite funny, but because of the randomness and lameness of the rest of the episode, the joike isnt funny.
Whereas south park has a story behind every episode whihch is either ripped off something or about something. i.e: two days before day after tomorow (day after tomorow film), mystery of the urinal deuce (all about 9/11), the jeffersons (michael jackson). And each episode is so in your face, its great.
South park has balls.