They regularly made fun of Bush 41, and I think those are some of the best episodes ever. Especially the Mr. Plow episode where Bush 41 orders Homer to "plow through" to protestors to clear a path. Or when he was Homer's neighbor.
But the episodes with Clinton were full of absolute mocking and ridicule of him.
Now South Park is a full blow, libertarian/conservative cartoon who spares nothing in going after the left. Sure, the right winger gets mocked as well, but most often, at the end of the day our side wins out.
Their absolute assault on the left is great. From Easter Bunny Reno, to Sexual Harrassment Panda. And let us not forget the classic Mecha-Striesand episodes or the "Crips" episode on stem cell research, which nuked Christopher Reeves. And the new classic, Crab People!
Family Guy is another outstanding cartoon. As if Futurama.