Depending on the program you are in my recommendation would be use some miles for a trip on the BA Concorde, assuming it resumes service. It is truly the ulitimate form of travel and will not be around forever and no replacment in the works. I flew both BA and AF (unfortunately not using mileage program) and the BA service is a class act all the way from being ushered through to a private check in lounge to the flight itself.