Fresh, clean metal deserves epoxy primer. It will not allow rust through and will take overcoats well (if properly prepped). People have reported finding epoxy primer in rattle-cans but none have reported back after using it.
Whatever you use, make sure it is compatible with whatever other sealers, primers, surfacers, etc and finish coats that you will be using (use products within the same "paint system" to be safest).
