If you plan on flopping more than once (well you shouldnt plan on it, but to plan on having a square cage post flop) design is #1. Dom is just insurance it wont be too out of square post flop. I flopped my K5 on Dusy a couple years ago and tweaked the hell out of my cage, HREW. A better (finished for that matter) design would have helped but DOM is stronger and would have minimized distortion. I am not saying HREW isnt strong enough (contrary actually) but I am saying DOM is definatly stronger and more uniform. Your logic that square is stronger than round is wrong. The flat surface area on a square tube will buckle before round will and thats the premise of why round is stronger than square. Your tubing is only as strong as the weakest point.
That is true, but will you really need that extra strength? Going 200mph in a race car sure, but cruising around in the woods and taking a roll? Im not rich, that DOM is twice the cost.
