Toss up between Simpsons and Futurama. Both deserve to be on there for longevity if nothing else.
Honorable Mentions: Home Movies, King of the Hill, Family Guy, and Duckman.
ETA: Loving the amount of love the Boondocks is getting. That show is phenomenal. It is amazing to me the creator is militantly liberal. His show seems to reach all audiences.
This post was edited on 2/14 at 11:13 am