I never really read the books, but I can answer based on the show. At first Serena seemed more appealing and I related to her more. But the more i got to know Serena and the things she did, the less I liked her. She is just a major trouble maker, even if what she does is unintentional. But I do understand why she is the way she is...She has no father figure in her life and her mother constantly blocks her emotionally and doubts her constantly, thus she moves from one man to the other to try and find a male figure that would approve of her. Blair however I hated her guts when she was still in high school, and she is the type of girl that always gave me hell when I was still in high school. But her relationship with Chuck was about the best thing that happened to her, because she truly loves him and that brought out a lot of her good qualities, and she is continually becoming a better person (as much as her kind can allow her). So the final verdict is...well...I like Blair best, but i like the complexity of Serena's character, even though I don't like the things she does or the reason behind her attitude.