Frank Costello was the politically smartest Don. I believe he was the model for Vito Corleone.
Politically scary. Every Politician was on the take back in those days, corruption was much more widespread. The mafia changed dramatically since Costello's heyday, laws have changed, organized crime has been viewed as a serious threat by the Feds, the media got stronger each decade and public awareness of the mafia went up ten fold. How would any of us really know who the smartest was? We didn't know any of those old timers, only the "small" sample size of literature out there. It's like trying to compare Joe Montana v Tom Brady(pre-Deflategate). It's impossible to truly compare, rules have changed, offenses have changed and defenses can't even touch a guy in today's game...hence padding the stats for today's QB's.
Costello didn't have to deal with RICO, TMZ, Investigative journalists and surveillance technology that is light years ahead of where it was during Costello's reign. And the government has rooted out "in record numbers" public/political corruption through tools like RICO and WITSEC. In Costello's day, protective custody was a joke, thus not giving informants much of an incentive to cooperate.
Meyer Lansky, Joe Profaci and Tony Accardo weren't slouches either, Profaci made a fortune in Olive Oil.
