Nel

When Nel says "I am me", she is transcending her history. She is realizing that she is more than just her mother's daughter, her grandmother's granddaughter, and she does not have to be like them or anyone else. She is realizing that she is her own person, and she wants to rise above what her mother and grandmother are.

While Nel's mother scorns her grandmother for being a prostitute, Nel scorns her own mother for accepting her supposed "inferiority" to white people, especially on the train. Nel wants to escape from the African-American stereotypes and create her own kind of person-- not based on her skin color, not based on her heritage, not based on what she's told. Nel wants to be herself, and she realizes that evening that she can be her own person, that she can be "wonderful".