Who do you think is the smoothest most fluid fighter? I vote Reymundo "El Rel" Beltran. Although I think he is up against it in Crawford.
I do like the way Chocolatito puts his punches together. Crawford looked pretty smooth switching to Southpaw and back, last time out against Gamboa too.
I don't know if he is the smoothest overall, but Billy Joe Saunders would be the smoothest white guy.