I think it's easily the Gambinos. Most of the big families had leaders "touched" at one point or another, but the Gambinos had multiple bosses or underbosses clipped.
Colombos: Joe Colombo, a boss.
Bonnanos: Galante, the 3 Captains(they were not leadership technically, but high ranking)
Genovese: Zeccardi, either a boss or a front boss, depending on who you ask
Chicago: Giancana, and maybe Nitti if you want to count him in, both acting/front bosses, depending on who you ask
Gambinos: Mangano, Anastasia, Castellano, DeCicco
I'm probably leaving out a bunch of high ranking captains but it's clear to me the Gambinos come out on top, or at the bottom, depending on how you look at it.
Montrose, I think what you've said is an excellent overview.
Personally, although I've posed the question, I, myself, have not evaluated each family and fully thought it through yet, but you may very well be correct in your assessment of the Five Families.
