It depends how you see. I love the square and am very happy with my 6. I am so happy I am looking for another body. It's my artisitic licence not to crop and print square. It cost more on paper for printing but I don't care. I love the square!
The 50mm is very wide for me. I think the 43mm is specialized and wouldn't be an every day use lens. But it would be great for landscapes with interesting foreground detail. Good use of a lens like this makes you feel like you can step into the picture. Bad use of this lens, (which is very easy) will just make your pic look distorted.
As for the other lenses, I think there all pretty sharp and contrasty. I have never heard of a bad lens on the mamiya 6 or 7 range. It all comes down to if you like shooting square or rectangle I think.