I've done this before but I might as well do it again:
Rogue is the definition of sweet. The withdrawn gloomy girl what yearns for interaction and that you provide, gives the her the stable foundation she's been looking for. She's perfect GF material.
Kitty's kinda vanilla till you discover her submission kink. Then it's a slow decent into depravity as you train her, especially with having no gag reflex. It's almost like a trainer game at that point.
Emma's all about class and then you deliberately catch her in class. Starts out in secret and ends with her stripping in the court yard. A repressed exhibitionist that you bring out and seems to have a sex drive to match Zeroes. Freud was right, we all yearn for Mommy.
Laura you wanna pet and give massages to and pet and train together in the danger room and pet and watch movies together and pet and just generally hang out together with. And pet. Plus energetic sex. And pet.
I honestly don't care much for Jean, she's kinda ehhh and I can see why Oni didn't care for her. A black hole of a personality and bitchiness, why deal with that when you can kiss/headpat/have sex with others that are far sweeter?
I kinda like to pick on storm, calling her a slave or "Black Mommy" is something she'd absolutely hate but 850 obedience means she has to accept it. Other than that she's sweet calling Zero her beloved. A relationship would last with her I think.
I really like Jubilee. Her power synergises well with Zero to the point that it's a co-dependent relationship already, you're just slowly discovering how lively and energetic she can be. Plus she already respects you by calling you Bro.
I was iffy at Gwen at first but she's actually funny and charming in her own 4th dimensional way. Much better than the comics, as she has an actual personality here.
Haven't done Betsy yet, just her intro and that she's British.
If you ask me to choose, I'm gonna go Harem Protag and say I can't. If you put a gun to my head, I'd probably eat a bullet before making a decision. Only picking Rogue or Jubilee for example would leave the other in a worse off state. Rogue might not be able to control her powers again and Jubilee would lose going out in the day time. There's an actual, physical need to being with two people. More if you want to heal the trauma in Laura or help Kitty discover more about herself.
So yeah, I can't decide.