Looking at bosses over the years you can really see the decline from brilliant, Machiavellian businessmen, who were more *likely* to fit the romanticized Hollywood version with supposed codes of honour, etc., to Bosses from the 1980's forward who were image and murder obsessed. From Bruno you get Scarfo, From Corallo you go to Amuso, and in 10 years you go from Gambino to Gotti, etc., etc. - the whole culture and mission of the mafia was inextricably changed. It not only became more public and therefore a greater target for law enforcement, but was also less likely to draw upon more intelligent recruits as traditional discrimination against Italians abated and other opportunities opened up to second and third generation Italians. With rare exception, they stopped attracting the cream of the crop.

All time Boss might well be Frank Costello. He may have been too weak to keep Vito Genovese away, but there's little denying that the organization itself would likely have been better off with Costello's connections and diplomatic skills to leverage them.

Accardo is a great pick. Gambino would be a great pick also.

In the modern era, Massino prior to turning rat deserves a mention, although he ultimately disqualifies himself. Vito Rizzuto doesn't get enough credit. Where even high-achieving Mafiosi would be looking to make millions, Rizzuto looked at rackets and thought about how to make billions. Then he did it, while unquestionably running a whole city and keeping the peace between rival factions and buying off all levels of government for two decades - and never once did he hesitate to pull a trigger. Anyone who he decided was an enemy all of a sudden had a very short expected lifespan.

In the here and now, probably only Barney Bellomo is really worthy of high praise.

I'm not considering any of the Italian bosses in my picks...that's a whole other milieu of which I am not well informed.