I used to like both equally, but now I think both are past there prime. The Family Guy episodes are starting to make no sense, (not like they did before, but just more so now) and I think they're definitely running out of ideas. And as for South Park I think they're just getting annoying, and the episodes are just not funny at all.
South park is completely stupid. I don't think that 12 year old going around talking about porn and swearing is funny at all. Family guy is one of the funniest shows ever created