Ky is the good guy. Sol is an anti-hero that doesn't mind to kill if he has to, and usually he tries to do so as it's the easiest way for him to achieve what he wants.
Slayer is a vampire that has an inmortal female partner that allows him to feed without killing or scaring anybody else and Potemkin's mentor. He also quitted the "Assassins Brotherhood" he started (or so, I don't remember well that part of the story) and he seems to be doing nothing but live and have fun.
You should read a bit of background before decide who is "bad" or "good" according to your religion