I have mixed feelings about South Park. It's clearly written by some clever and funny people, but I really don't jive with their politics, and sometimes they insert that into the show in a way that makes it really difficult for me to watch and enjoy. Scott Tenorman Must Die is a fucking classic, though.
You should definitely give Rick & Morty a chance. I am not a fan of Adult Swim shows in general, and I don't watch any other animated/cartoon shows, but the writing is *so goddamn good*. It easily gets my vote for the funniest - and most clever - comedy currently on television. It hits on a sort of middle ground between the weirdness of most Adult Swim shows and a more typical, structured narrative. The characters are a bit over the top, but not in a completely unbelievable (or perhaps a better word would be unrelatable) sense. There's some real depth to the relationship between the titular main characters, and each episode has an actual plot. Unlike, say, Family Guy, where a lot of the jokes are basically non sequitur sequences inserted haphazardly into the episode, the humor in R&M is situational and develops out of the actual plot developments in the episode. There are plenty of great asides and one-liners, but they are related to what's going on in the episode, not "you think that's bad..." I really can't say enough good things about the show, and there are less than two dozen episodes so far across the first two seasons so you can easily binge watch it over a weekend (or in one day, if you have nothing else to do that day - without ads it's maybe 7 or 8 hours of total content).