The second shot is made for a square crop, and it is a well executed image of a beautiful piece of artwork. .
The first and last images don't seem to reap any great benefit from the square crop--by that I mean that the fact that they are square, doesn't magnify the subject or compositional effectiveness in any significant way.
Thanks for your comments. For the first and third, do you mean that a different crop would be preferable, or just that the square one isn't obviously superior? The second was a no-brainer, but I experimented with different compositions for the other two before settling on the square ones.