Kind of a tough one, because i think Duchene at his absolute best has been the better player and has at least off and on, played the more valuable position. But he's also been wildly inconsistent. My recollection of Tanguay is just quietly churning out a ton of seasons of really good playmaking from the wing. So...tortoise or the hare, sort of.
I lean Duchene just on the strength of him at his absolute best being better and higher impact than Tanguay at his absolute best. But i'd definitely understand anyone voting the other way, on the strength of more consistency.