Choosing a camera for the rectangular format? Emmm, since I like shooting with a medium size TLR, just what camera choices are there.
Square is for squares! Just kidding. What ever you think is right is what you should do. The rectangle is more common I think, in cameras and paintings, but it really doesn't matter, a particular photo and the way you see it, is what you do.
There is nothing to prevent a person shooting with a 4x5 to crop and make prints, say, 8x8, if they think it makes a better picture.
I don't see this as only one way is right or if you shoot a certain way, you must get a matching camera. Two people may have different composing ideas, neither one needs to be wrong for the other to be right. Silly.