South Park. Not only is it funny, but beneath the humor is a pretty insightful point. It's funny and it crosses a lot of lines (more than Family Guy- look at the ending of "Scott Tenorman Must Die"), but underneath all that, they're actually trying to say something intelligent. There's an idea behind each episode, and they absolutely NAIL that idea each time. ANd they actually manage to weave an entertaining story around the humor.
Family Guy is a bunch of random, stupid jokes. Which admittedly are funny, but that's all it is. It doesn't earn its laughs the way South Park does. I still kind of like it, though.