It's a tough one because I love every character in the series, even Jorge (Ogre).

But I have to say Kurama. He's proof that looks are deceiving. You got a guy who looks and sounds like a girl and everybody doubts him at first (well, "everybody" being Yusuke and Kuwabara) when they go to fight the Saint Beasts. Hiei sets them straight by explaining that he would never want to fight Kurama because he gets vicious when he fights.

Sure enough Kurama proves himself to have a bit of a maniacal, merciless streak. But at the same time he's not a complete dick. For example he wanted to save his mother with one of the demon artifacts (the mirror) and stepped in front of Yusuke during the Yusuke vs. Hiei fight.

So yeah, Kurama all the way. The funny part is, his "parallel" in Hunter x Hunter, Kurapika, is my favorite character of that series.

EDIT: Nobody voted for Kuwabara. Poor guy. Well, I have one thing to say about that. A mulberry is a tree. Kuwabara is a man.