First off, "Hammer into Anvil" is a masterpiece. You can see the ending coming from a mile away, but it's the execution that matters. Honestly it's almost more like one of the episodes of Columbo with McGoohan in it—"By Dawn's Early Light" and "Identity Crisis." (Also McGoohan directed an episode of Columbo called "Last Salute to the Commodore," which is a bit like Columbo does "Fall Out.")
Anyway, as much as I love "Hammer into Anvil," I love "Once Upon a Time" more. McKern is such a good counterpart to McGoohan, and you can't top, "The lone wolf belongs to the wilderness!"