The Question and Answer section for Sister Carrie is a great resource to ask questions, find answers, and discuss the novel.
Carrie goes through the biggest change over the course of the novel. Unfortunately, in the end, she's come full circle and is no happier than she was when she left her parent's home.
I don't think I would befriend any of the characters in the story, but if I have to choose..... I'll choose Lola. She's real.... no pretension, no airs.
I'd have to say that Carrie is most motivated by the desire for financial stability or gain.