well what made you pick buster keel ?
For me it was that it is a manga that portays monster from the monsterside of view and that some at least behave like the wild animals they are supossed to be. keel is a wild dragon ape and behaves belivable
when he joins the human heroine its not because a change of heart from nowere it's cause he sees a chance to be free again, so far i have read this still holds true when he tend to like monsters more than humans with a few exceptions
plus the story os good and is not tototaly predictable so you know what will happen and who will win