in terms of goal scoring, a large favor goes to nash
Identical goal totals in the previous 5 years. Patty is a goal ahead this year. Of course someone will likely point out that Nash has never had a playmaker center, while Marleau frequently played with Thornton. Of course, I would than argue that Nash is THE focus of Columbus offense and gets the most opportunities. I would guess (though I am not good enough with behindthenet) to confirm that Nash starts significantly more time in the offensive zone and gets more PP time than Patty. Patty has a higher quality of teammates. Which leads to more goals is up for debate. Also, among active players only Jagr and Lidstrom (by 2) have more playoff goals. Zetterberg and a distant Hossa (14 back) are pretty much the only one who can catch him in the near future.
Give me Marleau for the better player, but if in a vacuum, I'd swap him for Nash to get a winger who is five years younger. In reality, I don't know that the shake up in the locker room would be worth it.
Nash is overrated. I do believe really good players have good numbers with any linemates. That being said, almost every star from bottom tier teams can't handle same play in better team (Richards, Jokinen, Bouwmeester, Kovalchuk etc.). Nash has serious career problem with winning culture.