My eyes are positioned horizontally in my head, giving a "wide" field of view. So a widescreen monitor always feels more comfortable. Unless anyone has a single, perfectly round eye in the middle of their face, I don't know why you'd want a square monitor. :) That's my opinion, anyway!
Any reference materials can be on the very edges with a very slight turn of the head or a big eye swivel.
I've heard that the "aspect ratio" of humans' field of view is approximately 4:3, so if that's the goal, you'd want...2217x1662. 1:1 is actually closer to 4:3 than 16:9. My guess is that the tendency to scan left and right rather than up and down is the stronger argument for wider aspect ratios than the human field of view argument.
https://en.wikipedia.org/wiki/Aspect_ratio_%28image%29#Pract...