In addition to having martial arts skills to match him, Ben's backstory contrasts very well with Bruce:
>Ben grew up in a middle class neighbourhood. Bruce grew up as one of Gotham's elite.
>While both are victims of crime, the way they are is in different ways. Bruce lost his family to a mugger, whereas Ben killed the man who tried to rob and (possibly) kill his parents when he was ten years old (this is often the age Bruce was when he his parents died).
>Bruce became Batman to bring justice to those the law could not reach. Ben became the Bronze Tiger to act out his rage and eventually turned to crime.
>Bruce while an accomplished fighter, is not above using pragmatic methods to win. Ben seems to favor the more 'honorable' approach.
In addition to these differences, both men have showed to struggle with their violent sides on many occasions, and I think that one thing they have in common sets up an interesting dynamic between the two. Maybe Bruce sees a chance for Ben to turn his life around (this doesn't have to actually happen, but the possibility could be there).
Also, both their names begin with a b