Ines from Steam Prison. He is a really nice, well-developed character and his relationship with HOUNDS is really interesting, but his route was a bit boring. There almost weren't any romantic moments between him and Cyrus, so their love just doesn't feel genuine.
I am a fan of slow burn and enemies to lovers tropes. I like it when characters first hate each other but then slowly fall in love with each other. As for the least favorite, that would be arrogant and selfish characters.
I really loved Yang's bad ending, because at first it seemed that everything was fine and Yang loves Lili, but then...well, it's called the bad ending for a reason. Also, pretty much all the bad endings in Butterfly's Poison, especially the ones with Majima.