I hope Hoppy spots this thread and weighs in with his thoughts. I am only familiar with the AH Supply reflectors which are very, very good. They use MIRO4 highly reflective (95% reflectivity) aluminum for both their power compact and 48" T5HO kits. I believe that Catalina advertises reflectors with 99.9% reflectivity.
That said, using quality aluminum for the reflectors is just a portion of the total equation; a properly shaped reflector, properly sized ballast, and proper bulb spacing also have a lot to do with the quality and quantity of light a fixture will emit.