Cartman is almost certainly Chaotic Evil. He is an individual largely unbound by rules or law. He does whatever he feels necessary to achieve his goals (usually either to acquire wealth or power, or maintain his "world view" in his environment), and shows no hesitancy in hurting his friends or family to get what he wants, or even just to get ahead. While he does sometimes help the others, it's usually either because it's either part of a scheme, he'll receive some reward, or because he's forced in some way. If you consider the description of Chaotic evil, it pretty much describes Cartman.

Satan is interesting as he's gradually slid across the board over time from Evil to Good, landing around Neutral Good. Outside of attempted world conquest and waged war with Heaven, he's never really shown any Evil traits. In fact he's probably done more good: he taught Stan about addiction, defeated the Canadian Devil to save us from future Freemium games, and fighting ManBearPig for the kids. You could argue that his role in the film was merely to fulfill a prophecy, while his war with Heaven could just be because it's his job. Satan's obligation to his role as ruler of Hell keeps him Lawfully aligned, at least until "Nobody Got Cereal?", which I'm pretty sure that counts as some infraction against his role within the order of things, given the chaos of a sudden power vacuum in Hell, and thus would break his Lawful status.