While I agree on some level that a character who sleeps with everyone won't be most peoples' favorite, I can excuse this in a fenoxo production (c'mon who DOESN'T sleep around in this universe
). I remember Savin joking in one of the backer updates that she was masturbation aid, and while that's pretty funny to think about that literally, I think that encapsulates her vision of what sex is pretty well. It might be that she explicitly tells you in the beginning that there's no chance of you two ending up exclusive that hurts people the most. It might've been easier if there was an option to make her attraction to other people implied rather than explicit.
That being said, I'm not sure Cait is my favorite character, but she might be my favorite character to read. She is
dripping with personality in every scene she's in. Ironically, while the sex scenes are well written, it's how she interacts with the world that interests me the most. If you lose to the centaurs while Cait is in your party, there's a moment where she holds your hand and gives you a sad smile, right before they give it to you. There's a dream with Cait and Kyoko which I won't spoil in case you haven't seen it, but her dialogue afterward is perfect. In the newest update she conjures Lovecraftian horrors not because she wants weird sex, but because she'll try stupid and dangerous things if it'll save her sister. It's the small details that sell the characters in this game; like you said, they feel like real people with personalities rather than a button to lower your lust.