I think Goku would win. Goku has a slight power advantage, and he has much more stamina because he's not fighting with anything close to his best. Piccolo's regeneration wouldn't matter; it's only useful for regenerating chunks of his body and doesn't seem to do anything for cuts or burns. Yes, that's retarded, but it's what we've seen in the series. Even if it was useful, it drains his power, which would widen the gap.