Asking about a favorite character in a novel with so many villainous or small-minded or hateful characters is in fact an oxymoron. "Favorite" is defined as a person or character or object that is greatly liked and viewed special preference (Collins Dictionary). It is difficult to say you greatly like a character that is described as:
- having dangerous genetic racist theories: Dr. Greene
- resentment for light-skinned black's affectations: Peter Fowler
- being violently racist and the superintendent of black schools: Jefferson Wain
- begrudging and as feeling superior to dark-skinned blacks: Molly Walden
- recognizing the need to disassociate himself from his mother in order to advance socially: John Warwick
- losing his love when he discovers African American ancestry in his fiancee's family history: George Tryon
While George Tyron might be forgiven and pitied because he relents after finding out how vapid and coreless Blanche is, it is certainly not possible to see the standard definition of "favorite" in relation to any of these other characters. The other exception might be John Warwick who was advised by Judge Straight to take a path in career and society that led him away form and required silence about his true family origins.
In light of the meaning of favorite, the choices for favorite characters in this narrative appear to be narrowed down to Frank Fowler, Rowena (Rena) Walden, and Judge Archibald Straight.
Frank Fowler is the heroic African American worker who loves Rena while knowing her background, who is at her side to care for her while she is ill and when she dies.
Rena Warwick is the heroine who finds that with her brother John's help she can "pass" as white in South Carolinian upper class society while finding love with an estate heir. She is rejected by him when she selflessly goes to her mother to nurse her through her deathly illness; after a time, she sickens and dies herself with Frank next to her.
Judge Straight is a kind and unprejudiced. He helps John understand the importance of setting up a life elsewhere, helps him get through law school and tries to help Rena.