Yeah, I'd go with Napoles for greatness. Top 5 welter trumps no. 1 jnr featherweight when you also factor in he was a top flight jnr welter too. Both had very dominant title reigns but that Napoles did it as a small welter makes it even more impressive. I'd say he was better too, although I think that's closer.
Napoles clear for me. The guy was a small Welter, more of a natural Light-Welter if anything and he'd pretty much established himself as the best in the world at 140 before he moved up, albeit he never got a title shot there. That makes his long reign at 147 all the more impressive.
Love both fighters. For me Napoles is both greater and a also a slightly better H2H fighter at their best.