Grabbing a half of a 'memberberry, the show doesn't play much about character personalities anymore. Technically South Park does what knows the best now, the topical satire. But well, once the continuity striked, the moment of surprise somewhat waned for me, despite most people not seeing it as a big deal. Anyway once it got a new direction after several first seasons, the personality emphasis was on Cartman, Kyle, Stan's family, Butters' background, Garrison and Jimmy... wait, they stopped using even Jimmy in the last seasons.
On the other hand the very beginning played on the characters' interactions - we had Chef, uncle Jimbo and his friend (they sometimes interact only with adults later on), Jesus and Satan, Dr Mephisto and his sons, Officer Barbrady (mostly replaced by more-dimensional Sergeant Yates), Veronica Crabtree, Al, Tweak, Wendy (the woman of South Park once she used to be), Pip, then there was a guy without legs everyone forgot about... and whoever else.
Then again seasons 8-16/17 rule the show for me.