What amateur BB contest had the most guys who later either became pros or had a huge impact on the sport? I'd say 1983 nationals certainly makes a case:
HeavyWeight
Bob Paris
Rory Leidelmeyer
Mike Christian
Matt Mendenhall
Rich Gaspari
Neal Spruce
Ron Love
Jeff Everson
Chuck Williams
Benny Podda
Joe Bucci
Mike Torchia
William Dabish
Charles Glass
Jon Aranita
Ernie Santiago
Dean Tornabene
Jose Guzman
Joe Dawson
