Whenever people say they dislike Family Guy because of all the random jokes I always like to tell them that they don't have the mental agility to keep up.

Not sure if its completley true but it never fails to get under their skin.

Family Guy 100%. I must admit though that I don't watch South Park regularly. But from time to time I catch a re-run and it's never made me laugh (except for the episodes from the first 2-3 seasons.)