Right now I'd say that Maya and Sage have the most depth of the main girls, but Sage only got that for me in the latest episode with her opening up to the MC about her family and how she doesn't deal with emotions very well. With Maya, we know about her Dad and the implications of his homophobic, uber-religious stance on her upbringing which builds a picture of why she is how she is. With the Bella, Jill, and Josy, there isn't very much there besides the looks and certain character attributes, but we still don't know much about them yet, whereas we know a lot about Quinn and she's been built up in a way that is making her someone people are really caring about.