I liek both characters.
Carth had really really great voice acting, and I could emphasise with the characters.
Atton had bad voice acting, but his prsonality was all an act right? He was also really funny and I liked his character, and felt sorry for him being manipulated by Kreia.
TSL did have much better writing and rasied alot of philisophical points. If I was to write an essay on either of the games, I would choose TSL, despite the poitns of remdemption rasied in KOTOR.