I honestly have to say that I favor Family Guy over The Simpsons. Keep in mind, I used to be pretty into the Simpsons, and I have seasons 1 through 11, as well as the 20th Anniversary 20th Season Edition from a couple years back. Season 1 of the Simpson wasn't that funny, it really seemed more like a test-run to see what they could and couldn't get away with on 1990s television. Seasons 2 and 3 began to pick up, and Season 5 and 6 were the pinnacle in my opinion, with seasons 7 through 10 also being quite good, and then downhill from there. The episodes where Homer goes to space, where Bart breaks his arm just as summer rolls around, and the Who Killed Mr. Burns duo were some of their best episodes, in my opinion. And just recently, a newer episode of The Simpsons was on, and I actually changed the channel; I've never done that before. The newer episodes seem to be dull and bland, with newer celebrity guest-stars sprinkled in. It just seems tired.
I got into Family Guy after I had been watching The Simpsons for a couple years, and at first I found it to be the most hilarious thing I'd ever seen. Several seasons purchased later, and I can see that the first 3 or so seasons were superior to any thing that came after that. I mean, they were just fantastic; they had a nice balance of humor, story, and never too many cutaway gags, unlike newer episodes. Later episodes of Family Guy have started to piss me off, with more and more cutaway gags that either just waste time with the characters dragging a joke out, chicken fights, or freaking Conway Twitty for an entire freaking song. Come on now. That said, I still find Family Guy to be funny, and it's aged much better than The Simpsons have. I also like American Dad, and the Cleveland Show is alright, but not great.