As i said before, Sicilian Mafia is much more brutal. Leoluca Bagarella is top spot for sure, he was involved in around 100-150 murders
Filippo Marchese, he was running "Room of death" together with Bagarella.
In terms of pure toughness though, let’s say if they fought one on one then I think I’d take the Americans just based on all of the great American fighters lol