I think South Park is morre juvenille as it relies on gore, shock value and foul language as it's primary props.
I went through a phase where I liked Southpark a lot, but it quickly passed.
At first I felt the implementation of "flashbacks" was overdone in Family Guy and they relied to heavily on this technique.
But I feel they've made it their own and created a new comedic technique.
Another reason I selected Family guy was because it is more "current" I have watched endless repeats of Southpark and the Simpsons and am just frustrated with their repetition.
American Dad just falls short of the mark.
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