rematche is right, without The Simpsons there probably wouldn't be Family Guy, even Family Guy has acknowledged that in their own way. That doesn't withhold me from saying that I think Family Guy is funnier however. Now I am a little biased, I haven't seen much of the Simpsons mostly because my mom wouldn't let me watch it as a kid, and it just never really stood out to me. Family Guy definitely relies a little too much on its gags and crude humor, but I still love watching the reruns and laugh every time I watch it, even if I've seen it before. I'd say The Simpsons was the king cartoon family in the 90s, but the 00s to the present were dominated by Family Guy all the way.
And if I can get a little off-topic, I think comparing Family Guy and Futurama would be a more interesting and difficult discussion then the old Simpsons vs. Family Guy thread. Oh, and South Park is greater than them all.