What is the best camera lens to choose for my bed size?

To answer this question requires one additional piece of information: The height above the bed that you plan to mount the camera.

The LightBurn cameras page has numbers you use to figure out the minimum height for each camera lens choice, based on the size of your laser bed.

If you have a 700mm wide working area, this the math to determine the minimum height to see all of it for each of the LightBurn cameras:

160 degree lens: 700mm / 2.7 = 259mm above the bed, minimum
140 degree lens: 700mm / 1.8 = 388mm above the bed, minimum
120 degree lens: 700mm / 1.5 = 466mm above the bed, minimum
90 degree lens: 700mm / 1.4 = 500mm above the bed, minumum
60 degree lens: 700mm / 0.825 = 848mm above the bed, minimum

This number is the absolute minimum required for the camera to see the whole working area. You will need to allow a little extra because the un-warping that happens in the software will trim a small percentage of the image away as well.

In general, it is best to use a narrower lens (smaller angle) if you can, because there is less distortion to correct, and therefore the accuracy will be better.