Mine counters are melamine. It is just painted particle board and does not stand up well to moisture, but my counters are all dry, so it has not been a problem. Formica would be nice. Something smooth, no static, light color. Static can be fixed with staticide. Plywood with a sheet of mattboard over it would probably be fine.

My enlarger baseboards are birch plywood that are varnished. These I recess to the same level as the countertops. If you can wall mount your enlargers and have one big seamless counter, this is best. Use plywood and paint it white.