The Simpsons haven't been that great lately, and Family Guy isn't as good as its first seasons either. But right now, Family Guy is funnier.
But as far as a show goes, I still like The Simpsons more. I think the older episodes of The Simpsons are WAY better than Family Guy. The biggest difference I see is that The Simpsons are much better at telling the story while adding humor to it than Family Guy. Family Guy gets really random and the side jokes (like things that happened in the past, that have nothing to do with the episode) can be kinda annoying -- especially when I have no clue wtf they are talking about.
So overall, The Simpsons is still the show.