SouthPark is neutral to me because of the extreme satire they usually do, as the show's first priority is to offend everyone. I actually think you could see any slant you like to South Park, depending on the episodes you watch. There's "SouthPark is Libertarian" articles google has found me, but reading around more I find that those omit the episodes and episode details that weren't libertarian and focus on the ones that were. Some of the episodes do have a slant, but it's not consistent between episodes. Surprisingly deep satire juxtaposed to the extremely crude nature, some of the South Park episodes I consider nearly art.
Yes, it takes shots at most people, but from what I recall, it consistently portrays characters who profess some idea that falls under the creators' beliefs (which appears to be pretty solidly "mainstream" libertarian (as in, not tinfoil hat militia types or objectivists), though naturally it expands out of politics into just personal opinions, too) in a positive light, while either portraying characters who oppose those views/profess views they oppose negatively, or having characters who are consistently portrayed negatively (like Cartman and Garrison) profess views they don't like.
And yes, sometimes it is just a scorched-earth-wacky-obscene-fun-fest.
Oh?
They didn't portray Dawkin in the grandest of light. Matt and Trey are in favor stem cell research though they used it as the mechanisms for a villain, and allowing it to do some oddly ridiculous stuff.
They don't portray the Priest in the town as anything horrendous either, and they made Jesus both a wussy and badass.
No one likes Kyle mother, but she a big fat bitch, as the song so well describes, that not from her supposed political views, but because she a big fat bitch.
They also don't even portray science all that well. One of their longest running gags is a geneticist with giving animals more then on ass. They like science, and they are skeptics, being frequent goers to the Amazing Meeting.