If you're in a multi-year league, stick with the younger guys like N.S. says - more production for longer time, and better trade bait if you need it.
Couture has good production now, but his trade value is less than these other young guns.
Keep Seguin, Eberle, Duchene. They carry more value than Couture and even if you don't fully believe in them, what you could get in a trade for either is worth much more than what you get in a trade for Couture. Can you please answer my q about fantasy sleepers and busts? Thanks!