Suprisingly I like 6x6, 6x17, 6x9, 5x4 and also 10x8 with no prerefence, but I always shoot to the format and don't crop,

For years I used a 6x6 and cropped but switching to 645 and 5x4 I began shooting to fit, going back to 6x6 I thought would be difficult but I love it.

So no real prerence.