Until about 10 months ago, i would have answered the question this way:
I have shot 6x6 for the past 35+ years. My shooting has become slow and deliberate, especially on composition, so I am not surprised that 99/100, I like the square image and print it that way. My son, who has a much better printing eye than I have, however, often prints my square negatives in some rectangular version.
Then 4x5 came into my life. For the past 10 months, I have been trying to make something out of the 4x5 format. I can make good technical exposures (density, exposure) but the images have no life to them... no compositional value. It has become entirely frustrating to the point where I have begun to say the dreaded words: I think I should get rid of this camera and all the film and accessories I have accumulated over the past 10 months. (My wife just laughs...)
After this experience, I think I actually see square. I have pictures ...same content, same tripod position, even the same film in some cases... where the 4x5 image is boring and the 6x6 is great. So I can no longer rationalize it the way I would have. I think that some people (me!) actually see square.