I'd say the Simpsons was still funny for a few years after it put its name on everything (which wasn't that long after it started, really), but it stopped being worth watching about ten years ago now.

Is Family Guy still popular? I got the impression that even its fans found it rather tired by now. I think it reached its height about three years ago, at least here in North America. Personally, I've found it to be pretty terrible. There's about one brilliant joke an episode and the rest is just an exercise in being uncomfortable...

There's been just as much Family Guy merch been put out as there is Simpsons stuff, anyway.