Good lord. If they had done it, Mouth of Sauron on steed statue holding Frodo's mithril vest, easily.
I could choose Bilbo, as that was the very first statue I got, or Orthanc, as that was my most searched for, but just for sheer WOW factor, and size, and iconicness (new word?), it HAS to be the Ringwraith on Steed statue.