If you think Simpsons has more meaning, morals, social commentary, etc, you're not looking hard enough. The first seasons of Southpark really sucked, but they're excellent now. It isn't pointless violence or swearing to entertain, its to show meaning through ironic truth. Southpark seems to use reverse psychology. They show the negative things in life, but with an ironic twist, allowing you to see the true meaning. Then just add in comedy.
The only way it would have a negative effect is if the people watching are ignorant, which is why I don't think immature kids should watch it.
In terms of laughs... hard to say, probably the older Simpsons. Overall, Southpark. And the new Simpsons... ugh.