Family Guy was funny, but has hit a quick decline sadly. The Simpsons was great in it's early years, but for the last 4 years at least it's only pitifully unfunny and obnoxious jokes with no regard for character, subtext or story. I can't get through a single episode nowadays without changing the channel in disgust. Example: That evolution one. What was with that? Springfield is a christian community for like 15 years, then one episode they decide that no, it was just Flanders and Lovejoy, the rest are atheist. What happened to all the church themed episodes? Lisa's whole spiritual guidance/buddhist developments? And the one where Homer's mother dies...they ALMOST had a reset to character driven and emotional storytelling, (the chance was right-freaking-there!) but they revert to pointless joke setups and disregard the notion that maybe something serious happened that could be explored instead. Mourning = emotional, not joke-filled adventure. And they have the audacity to claim the Simpsons is only getting better?!
Ergh...I digress.
Futurama is consistently funny and can get a laugh out of me, which is more than I can say for the others, so it gets my vote. Haven't seen the latest of episodes, but the recent ones I've seen have not disappointed me.