Hi,
my father had YashicaD TLR (6x6) and I've got as a small boy the russian bakelite Smena (=exchange,shift) for 24x36 (seems to me that still it had better lens than todays small Minolta which my son uses :O).

At the high school I bought Pentacon SIX (6x6) from Eastern Germany with Karl Zeiss Jena lenses and later a 180mm Sonnar to it. My wife has an older Exakta 24x36 and I bought an interface between it and my PSIX lenses. It was cheap and the Exacta is more handy, but still I am returning to the heavy PSIX. Probably it is because of my father, but the MF square format looks better for me.
The PSIX is not that good as Hasselblad or Mamyia, but the Zeiss lenses are pretty good and I am very satisfied with them. But for sure if I had possibility to try one of those other cameras, I would not hesitate at all :O)

Pavel Hampl