I haven't been watching either for several seasons now, so I guess I shouldn't comment, but this is the internet so hear me now and GFY.
At peak, Family Guy was probably better for total jokes in an episode and laugh-out-loud funny jokes, more on a shock level but also inventive wordplay and reference ideas. Closer to some of the memery from the internet and largely pre-dating it.
At peak, Simpsons was better for underlying cleverness and social satire, which was ultimately more satisfying to me. The jokes were more thoughtful and not always causing as much of a knee-jerk, gutbusting reaction, but the ideas were longer lasting. I still think of Simpsons quotes all the time in relation to things that happen in real life. Rarely do I think of that many from Family Guy in that way.
Advantage: Simpsons