It's a tough call, as Carlo has the edge in longevity and Luciano has the edge in vision and the right allies.

Carlo probably exercised more power than Charlie though. He had Eboli whacked, possibly helped setup Genovese, had Bonanno banished, instigated the Gallo-Profaci War and probably had Colombo hit, which essentially led to Gallo getting hit, and starting another civil war in that family, none of which that family has ever really recovered from.

I have always been of the opinion that Luciano's power stemmed more from his alliances with the Jewish Rothstein and the Irish Dwyer and Madden. His influence within those organizations, which, through the first half of Prohibition, were the dominant mobs in NY. Lucky using his contacts in these groups while working for Masseria are what made Masseria the 'most powerful' boss in the city after the other groups started imploding. But, imo, Masseria's power in that latter years of Prohibition stemmed directly from the influence Luciano and his boys provided. Masseria became the most powerful boss because he had Luciano.

That's just my opinion, still trying to find the right info to back it up.