>>43299978I'd probably say it's tied between Butters, Kyle and Randy.
Randy seems to just be involved with absolutely everything, which is constantly bringing him into focus, whilst both Butters and Kyle are trying to do good.
Butter's naivety leads him to be the one tending to do good.
Whilst Kyle does it because he's kinda an asshole, but wants to claim moral superiority. His rivalry with Cartman almost always leads him to good or moral choices, which kinda make him the default protagonist, because Cartman's machinations make him the antagonist.
