Well, I bought the game because of Grace, then kept playing because of Gabriella, and eventually got stuck with Sophia. I wouldn't say her 1st place is set in stone (I really like Gabi) but so far she is my main girl too, I sure hope for some decent romantic ending with her. I think Sophia crying scene (in her sleep) triggered me to finally give her path a go which happens in a game regardless.
Out of two twins Elizabeth is, well, not evil, but I dunno - bad girl?, also let's say arrogant and more dominant, so I basically see her route as a "bad one" and Sophia path as a "good one" or rather "neutral".
So, the confusing thing for me was a scene with Julia on a plane - to get on Blue path you should be a bad guy (well, not bad but perverted one) - you can get her route only if you creep on Julia. In the meantime - to get on the Red's route (which looks like an evil one) you should be a decent guy and respect Julia. To me it looked like variables were mixed up.
As for Sophia, I think she doesn't belong to where she is, she want's to be different, wants to get out of her sister shadow. (I got quite a de ja vu, I think discussed this with somebody). Anyways, I haven't played last update yet, still, I want Sophia to confront her sister, I'm sure she has some leverage over Elizabeth, some dirt maybe.
As for Ruby, I like how easy going and playful she is, around her you feel relaxed, and under different circumstances I would only consider her a Bro, not a GF, but here, I dunno, I guess I find her very attractive in addition to her cool personality. Also her explanation of what "harem" is and the main principles of AVN is one of my favourite scenes.
P.S. I apologize for my probably gibberish english, just woke up recently and drinking my morning coffee.