probably foil rings
From the Movie Block collection, it is almost certainly the foil
The One Ring, Answer to All Riddles, with Islidur's Bane and
Such a Weight to Carry significantly behind. But you also need to keep in mind the rarity of the sets in terms of printing. Realms of the Elf Lords, Battle of Helms Deep, and Siege of Gondor were all short-printed relative to the other sets, making a few of those foils a bit tougher to acquire.
Of course, this all pales to the late set Masterworks foils. Sets 15, 17, and 18 masterwork foils, like
Beorning Axe (O),
Gwaihir, the Windlord (O), and
Aragorn, Thorongil (O) are all very tough to find and regularly price competitively with some of the foil rings.
-wtk