: I've got all three and any paddle can be used with a wing type stroke but
: either the GP or the Euro are unstable with that stroke (tend towards
: fluttering)

Your GP - with your technique. Not true for others.

I also have all three types, plus Aleut, and a type no one here has tried that's a hybrid of Aleut, GP, and Wing and is used with a full on wing stroke (damn sweet paddle).

I rarely make such bold or absolute statements as the following, but anyone with flutter issues with any stroke with GP (or any paddle for that matter) has technique issues. 2 minutes on water with you would both prove this and end it.

Flutter - or alternating load shedding - is a result of a sloppy application of attack angles and/or overpowering paddle blades while accelerating at lower speeds (I've yet to hear of a case of flutter over 5 knots!). There are several small technique tweaks and "tricks" that are very natural, and a bit different with each paddle type, and once found you'll never have flutter issues again with any paddle.

For wing stroke with a GP, the natural cant from a grip mostly on the blade roots takes care of the attack angle with no conscious effort. Stroke is a "modified wing stroke" due to closer hand spacing. With a euro, you need to make sure the blade is climbing a bit through the stroke. The wing paddle does this automatically.