Carlo Gambino IMHO, He never let his emotions affect his decisions,and over the years built relationships with many future Mob heayweights.
He played a large role in helping establish the "Commision".
He was content to patiently sit back,observe,and bide his time until further advancement opportunities arose.
He could then be very swift and ruthless.

Other than minor jail time,he dedicated himself to living and breathing Cosa Nostra.

It was said that he never ever spoke about incriminating matters
If he wanted a man killed,he would do things like lowering his eyes or sighing when the man's name was mentioned.
His minions knew exactly what he was asking
He very rarely made a mistake,and I think it's ironic that near the end,he made one that not only was incredibly careless,but did grievous harm to his legacy.

I'm speaking of course about Big Paul,which led to the Gotti debacle