I have to go with Family Guy. I grew up on the Simpsons, no doubt about it. I have a lot of old episodes on tape. Hell, I didn't like Family Guy during it's first run. I was one of the people who said "It's a Simpsons rip off, I'll never watch that shit!" I watched it a FEW times during it's first run, but it didn't grow on me, mainly because I only saw maybe two or three original airings.
But then, just out of pure curiosity, I watched it on Cartoon Network and fell in love. I now own all three seasons on DVD and plan on getting the next seasons when they come out.
Family Guy just has that 'something'. I get many more laughs out of it than I EVER did with The Simpsons. There will always be a special place in my heart for The Simpsons, but Family Guy will always rank up at the top two of my favorite cartoon series list (the other being South Park), unless something else comes along, and I don't see that happening.
Here's to you, Pea-Tear-Griffin!