I have to admit, I am one of them. Octavia is definitely my favourite due to my weakness for "damsel in distress" trope. There's an interesting power dynamic in her route; as a teacher she has certain power over you, her pupil, which she's shown to utilize (for your own good),
And in both scenarios - whether you decide to help her or to expoit her - she gets to know that you are aware of her secret, ergo you get power over her. And I don't know what it tells about me as a person, but I really enjoy that. In fact, I have a feeling that I would get more satisfaction from helping her rather than just from watching h-scenes with her. Claudia comes close second, because who the hell doesn't like Claudia. You have to be a monster not to like Claudia. Even Victor likes Claudia. Honestly, she's designed to be liked (much like Marcello is designed to be hated).
So far Riley's route feels to be the most realistic to me. Claudia is just too perfect to be believable, she's always so sweet and caring, it's like she's completely incapable to get mad at MC or anyone else. Octavia is a "princess in need of a savior", and while I love that stuff, her desperate situation feels kinda melodramatic. Karen is your regular "slutty MILF"; adult games are full of such characters. Compared to them Riley as a character and the romance with her are the most life-like experiences in the game. No drama, no taboo fetishes, no exploiting, just two inexperienced teenagers trying to reach out for each other. Flirting clumsily. Doing things like asking out a lady in an evening dress to a pizza diner. It's like they are not characters in an erotic game, but real human beings.
Same here. What I really like about MT and its characters is, among other things, how no one just jumps on MC's cock because he and his cock just drive them mad with lust. Well, Karen kinda does, but you have to have someone like her in a porn game, right.