That's it in one. I've got the first nine series of The Simpsons on DVD and I still laugh when I watch them despite having seen every episode at least five or more times. That's a sign of a quality television show.The Simpsons hasn't been good since 1997; however, from 1989-1996 it was not only the greatest animated show of all time, but one of the best television shows ever made.
As for the poll, South Park without question.