I hate the Simpsons. I used to love it, but now, if you watch the newer episodes, you'll realize that it's no longer anything more than a commercial. Every joke in the show contains some kind of corporate advertisement. It's not even funny anymore, it's just annoying. I was watching an episode yesterday, and in that one episode, one of their jokes contained the words "eat at Arby's", and another one contained the words "why dont you check your local yellow pages?". And that's just two examples off the top of my head, the list goes on and on.
Family Guy is still fresh, and fairly new. It has a couple of guest appearances, but mostly the show relies on it's comedy.