Yes, flat CRTs are easier on the eye than non-flat ones. Buy a flat one if you can afford it. On a non-flat tube, images are distorted and lines look curved.
However, today's non-flat tubes are much less curved than those of several years ago. So if you're on a tight budget and are not doing any critical graphics work, non-flat displays are quite acceptable and the eye quickly adjusts itself to the slightly curved image.
