book 1:
I don't have any preferred scenes on any of the routes, it's a book that I don't like very much.
book 2:
girl: azula
route: love
scene: cowgirl
It is a scene that I like a lot, because Azula is completely submissive, marking from that moment his total dominance over her.
book 3:
girl: toph (obviously)
route: slave
scene: cowgirl with big breasts and audience.
Toph for me is the best character in the whole game, I like all of her scenes, and I loved her huge breasts, and katara, suki and ty lee being together, it only improves the scene even more. I would say that better than that, just if june, joo dee and lin were there too.
book 4:
girl: jinora
scene: blowjob
This scene is my favorite, simply because I have been waiting for scenes from jinora for a long time, and I'm hoping for the next update to have more.