I like them a lot because of their internal politics and their friendship. That's why I like Nobunage, he's not just a straight up evil, he see's the potential in people, and cares a lot about his friend. They're not dehumanized, even though they're killers, they just don't mix up work and their personal life. Also, they're not just all black evil killers, if all of them would act like Feitan and Phinks, I'd be tired of them after an episode or two.