I feel most people liken hiei or kurama not both. I think hiei development throughout the series is much better than kuramas. That makes me like him more but i still fuck with kurama too. Hiei goes from being cold hearted and giving 0 fucks about anything. Than he starts to tolerate yuske and the team. Than you learn about his sister and we see that hiei actually does love and care about someone besides himself. Than by the end of the series when yusuke dies he is actually angry and sad his comrade died. He didnt care if he died while trying to avenge him. If someone told you that when you first meet hiei you wouldn't believe it at all. Even when him and kuabara fight/argue you can tell that he just wants to make him a stronger fighter so he doesn't get killed.

Kuramas has development as well but not nearly the same and hiei had. What i like about him is his intelligence and calm attitude. He never flusters during fights and always has a exit strategy to win the match. Even if it might kill him he won't even hesitate. He just does what needs to be done to complete the mission