In NYC, The Genovese Family has traditionally been the largest in terms of numbers for most of that time period. They get my vote for most powerful.

IMO, the Gambino's had equal power during Carlo's reign, from the early 60's to the mid 70's.

Outside of NYC, Chicago is the only city to have anything that could rival the Genovese and Gambino borgata's.

I think any attempt to compare a non-NYC family with a NYC family is futile. Apples and Oranges.

Let the debate begin.