Centurion lounge first, then the Clubhouse. In the Centurion lounge, you might want to try the Speakeasy as well as a seat that's convenient for food. (I'm not sure whether JFK has an inner sanctum or special reserved seats for Centurion cardholders, but if so, be sure to pick those seats.) It's better to be in your airline's own lounge closer to departure in case of delays, etc.