Stan is neutral his good motives are motivated by selfish thoughts.

If selfishness from time to time prevents someone from being considered "good", that basically precludes everyone. stan has the most empathy of anyone on the show, and probably more than most people irl.

Good

Definitely a good person.

One of the proofs that Stan is good is that he wanted in "Whale Whores" to save the whales

Stan’s not good he’s very selfish but he’s not bad so neutral fits him

By South Park standards he is good. IMO he is slightly above Kyle. Neither are great even by South Park standards.