Fiberglass service doors have many advantages over steel doors.  The first thing people see is the visual positive with the wood grain look embossed into the panel.  These doors can also be stained which enhances the wood look if that is being sought.  Economy Garages used to stock steel doors, and our number one issue was how easily they dented.  Dented doors after moving to fiberglass are no longer an issue.  The final big point I would like to make is the thermal value.  Steel conducts cold much faster than fiberglass which is an obvious advantage in our northern climate.