Lex Luthor: 10.1 Billion
Bruce Wayne: 6.5 Billion
Forbes also includea a further comparison of the two men.
Although in fairness, it isn't as if Forbes is the authority on lists of wealthy people, oh wait, it is.
It's simple people, Luthor's extracircular activities, aside from the anti-Superman vendetta, are designed to make money and are not always foiled. Wayne's don't make him a dime even when they succeed.
Credit to lilinthra for finding the list.