Both of them really have quite alot in common. Neither have superhuman powers, both became who they were based on the deaths of their families. Both are rather dark characters although I give the darkness edge to Batman anyday. I guess the main difference is obvious, Bruce is a wealthy playboy with many tools and a cool costume whereas Frank is just some gun toting psychopath. Honestly these two would be better partners than enemies but let's say they wanted to kick each other's asses, who would you vote for?