South Park by a mile, tbh. Seen every episode of all three shows listed in the title besides the new Simpsons which are crap and they don't come close. Family Guy is going down the drain with the writers obviously running out of jokes (although it is still high quality) and Simpsons has been horrible for ages.
South Park on the other hand stays as fresh as ever with insightful political and social commentary together with hilarious jokes. It's not really the quota jokes like Simpsons and Family Guy, that require four a minute to stop people getting bored, it's the kind of jokes that build up through a whole episode for a massive payoff at the end. I can't think of any show that has been going as long as South Park that has been so consistently brilliant.
