Well, we're all entitled to our definitions of "great." But Capone, while he deserves credit for creating a huge business in Chicago and acquiring major political power, screwed up big-time. We all know his story, but it ended with him spending 10 years in prison, and losing his mind to syphillis. According to John Kobler, one of his biographers, he could have settled his tax beef with the government painlessly but wasn't smart enough to take the opporunity when it was presented. And one of his doctors suspected syphillis early on, when it might have been controlled, but Capone turned down a spinal tap because he was afraid of needles. Lawrence Bergreen, another of his biographers, believes Al was a heavy drug user.
I go with Frank Costello and Carlo Gambino, both of whom were the most powerful Mob leaders of their time, and both of whom died peacefully. Frank served only a little time on a minor rap; Carlo never saw the inside of a prison.