South Park si better because it employs an actual plot and each episode isnt full of random things to fill in the 30 minutes they have. Family Guy ay have funny parts, but Southpark is better
Like Vengeance00 said... South park rolls with the same joke and keeps going with it the whole episode. Which could keep people watching or it could turn people away, It just depends on what kind of viewer you are.
Family guy keeps 2-3 major jokes going the show which again could keep some going or turn them away.
Personally I prefer Family guy but I canw atch both.