The flat ones are from Sony (trinitron) and Mitsubishi (diamondtron). Those companies made all the flat tubes, also for other brands. They have a different shadowmask thus a different image. Its not a real mask, but thousands of wires running from top to bottom. As the wires are on tension, these screens do not suffer from distortion caused by temperature differences. The images are more rectangular and a little sharper.
The curved displays are mostly slot mask or tridot mask, which gives more fuzziness.

Both will focus good at arcade resolutions. Trinitron corners will look fuzzier only at 1024x768 or above. Not a big problem here. The curved displays look more authentic, but the flat ones have better blacks, less reflection and easier bezeling.