In italy Matteo Messina Denaro can be considerated rich but the Barbaro ndrine was the most powerful especially in north italy and in Australia (a member of the ndrine Robert Trimbole killed the politician against the weeds Donald McKay in 1977,this episode was portrayed in Underbelly tv serie) and had ties even in canada.

In the US you must consider state by state and even city by city: in NY Barney Bellomo while in some part there are the bikers or the gang that are the most powerful. But if I would make a choice I would say that the Mexican cartels and their allies are the most feared and powerful in the whole US territory.