I don't think there are any absolutes in any of this. Mick's comments are good, posture, boat fit & technique are the key. Provided the length of a wing or euro paddle is correct for you in a particular kayak, in my experience I have found that you can then select different blade sizes to effectively 'gear' your stroke for different sea conditions. This does require that you possess at least two different paddles, but I would consider it appropriate to carry a spare in any case. I can't really comment on Greenland paddles, as I have yet to develop any real understanding of the correct body mechanics to be applied to effectively use this type of paddle. Happy paddling all, have fun out there!