For Me it would be Roy DeMeo.
The guy who was a perfect family man and the neighbour from heaven hosting barbacue's and 4th July parties for his neighbourhood yet at "work" he was the devil himself.
Leading one of the most atrocious crews in Mob history.
A terrific earner and a nasty killer.

Another intriguing guy for me is Tony Mirra although not much is known about him other than he was a nasty bastard and an accomplished killer who even other wise guys feared - he also once took part in group sex involving an up and coming young hollywood actress (rumoured to be Goldie Hawn!)

Gerrard Pappa although again not to much is known about him but he did once clip a guy whom he despised and just for good measure he buried the body under the foundations of a new building taking care to ensure the victims head was placed exactly underneath where the toliet would be!!!!!!!!!

Carmine Persico as others have said obviously has something about him to still be a boss after all these years - he's been a major mob figure for years and years