best in my opinion
Grey Student
Green Lolita
Blue Lady Vamp
Pink up for debate
I think they're all pretty debatable. Depends on how you're using them, and what you have to combine them with.
For green, in addition to Lolita, the Nurse and Trainer can also be good. And for items, I like the diamond ring and the egg.
For blue, there are quite a few. In addition to Lady Vamp, there's also Hippie, Sports Girl, Proctologist, and Police Officer that are all pretty good too. For items, I like the Thinker. There's probably more that I don't know about, since I don't have a ton of blues.
In general, it seems like girls that inherently have Butt Plug and Masochist work best for me in slot 1, and it can be nice to have a card with Silicone to drop on turn two. And if possible, it seems like Marijuana and Bomb are both nice combo effects to shoot for. But I'm not too far into the game, so I dunno whether or not my methods will be valid later on.