Napoles was a better welterweight, period. In a P4P matchup it'd take Pete, but at 147 Napoles wins competitive but clear.
I was never a fan of Napoles nor of Sweet Pea, but I give the edge to Whitaker mostly because of his amazing defense.
At 140, it'd be perfect because Napoles was really at his best there and Whitaker was closer to his best there ... interesting matchup to contemplate... Both with exceptionally difficult styles to crack