Alch old armor - don't do it after you needed it! Save resources for pimping your current/future sets.
NPC old armor - not worth it. Elements fetch more, so destroyer rondo, ftw. - sell the elements, or use to alchemy a needed piece of equip.
Stalling old armor - better of the choices you have listed, especially if blues or in high demand (especially 3rd tier heads/legs/chest pieces)
