My favorite board is neither one............. for the conditions you describe
I go for the 5'9" Kontact...it is a chop killer...the EZiest there is for the knees
Nothing tracks through chop like that board...with minimum bounce due to it's narrowness and shape
Works like magic for me at 75kg/165lbs with my 10-8-6 and 5 Rebels...from 20 to 40 knots
Ocean surf chop......intracoastal river chop.....that board rips it...and keeps the knees happy for more
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That's what I was getting at. Slimmer cuts through chop, so this is way to go. You are constrained by your knees condition, so what waves you kite in is pretty irrelevant for board choice. Best small wave board, whip? = worst board for your knees.