We've been chattering about this issue on photo.net - how best to fashion a portfolio for gallery presentation.

There are some strong arguments in favor of using a single *paper* size for all prints. For example, a stack of 8x10s regardless of whether the print are itself is square or makes full use of the horizontal/vertical space.

Also, some say that a stack of prints, unmounted and with no tissue interleaving, is easier for a gallery owner/manager to sort through.