South Park, hands down. The Simpsons was great in its prime, and would really give South Park a run for its money, but it's gone downhill since the early-mid 90s. Family Guy is funny every six months or so, but the simple fact is it's the exact same style of joke over and over again, and the predictability just makes it stop being funny pretty quickly. On top of that, South Park can be completely random and out there, or a fantastic social satire, and it does both of those things far better than Family Guy or The Simpsons.