How can people forget Hiei? The guy was probably TOO badass for his own good and despite being the more cold-hearted, ruthless of the group, he still had an honor code of his own and developed pretty well within the series.
Let's also not forget Aoshi Shinomori. He probably one of the most dangerous characters in Rurouni Kenshin. He's was willing to go so far to prove that he and his clan was the strongest and even when he didn't win in the end, he NEVER whined or complained.
In my opinion, both of their badasses beat Vegeta's by far.