Steel vs aluminum DIY shade sail pole

Hi all,

I’m putting up a shade sail and am installing 10 foot poles. Because of my application, the poles are going to be removable and ideally lower in weight. I’m thinking 3-4” diameter or so. So my question is this: what material (aluminum or stainless steel) and what geometry (circular or rectangular), would give me the most rigid pole for a given weight?

My intuition is that you’d want a rectangle with the long sides opposite of the tension of the sail, right? And it seems like aluminum is 3x less stiff but 3x lighter so it’s kind of a wash?

Thanks!