Eric, I really don't think there's a format you "should" use. I think you have to follow your heart and use what feels right and results in the least amount of chopping possible. For me, I was always chopping off the end of my 35mm frames because I naturally see square. Since squares are becoming more popular, it's much easier to find frames and mattes to suit them.
Of course, if you're doing commercial work that requires a specific format, then you have to consider that. Otherwise, do what's you.
Thanks for the grin. *lol*Who are some well known photographers (besides you Cheryl) who use square format rather than 6x7?