Noumin, thanks for the graphic comparison. Looking at your examples, I feel that the two end shapes (the square and panoramic) have the most visual impact per unit area. If I as printing those different shapes for a consistent feel to a show, I think I would tend to make all the vertical dimentions of those shapes the same, and not worry as much about the actual area...though the panoramic format might have to be different. Then it depends on how the images are displayed -- how close together, grouping same proportioned images together, etc.
And Bowzart's "If you can't or won't design within a specific bounded space, you can or will do NOTHING in this medium or in any other." is right on the money. It is what I meant be "filling all the negative" in my previous post.