I think there are probably four guys in the coversation

Jimmy Wilde-Perhaps the greatest p4p puncher the sport has ever known, The division was more or less created for him. Tiny even for a flyweight. Arguably one of the ten greatest fighters in history.

Pancho Villa-A whirling dervish. Wilde's successor. Defeated Wilde but Wilde was long past it. Dead at 24 with 90+ wins IIRC

Pascual Perez-1950's champ. Ten defenses. Under 5' tall, an attacking machine. Another 80-90 win guy

Miguel Canto-Unlike the other three was not a huge puncher. An excellent boxer and he had something like 14-15 defenses.

In my view the best answer is Wilde. Had Villa lived longer he certainly had a chance to pass him because in the early-mid 1920's the 112's got absolutely loaded with guys like LaBarba and Genaro and Panama Al Brown (how does a 5'11 flyweight grab ya?). Pancho would really have been tested but he could also have rolled up some awfully big wins.

Here's one other thought. By the time Finito Lopez rolled around men were getting weighed in the day before. On a same day weigh-in basis? Finito probably belongs in the discussion. He was taller and longer than anybody I've mentioned except Al Brown.

Nice question BTW!