This is a tough choice. Like I think I mentioned before, I'm not a fan of the complexity of Scarecrow, but all the others have a nice combination of simple wording, interesting effect, and good theme (and look, there's nothing fundamentally wrong with Scarecrow, I just don't personally like it). If I didn't vote for all of them in the first round, I certainly should have.
I do disagree with Showman's creator's comment that there's no Peddler variant in Cornucopia - Tournament is technically a Peddler variant in the early game, even if the main mechanic of it isn't really the Peddler but the Black Market variant aspect.
I think Scarecrow is a little lower risk than its creator makes it out to be - of course you can't use it effectively in the early game, but later on it has enough cycling as well as the Actions necessary to really benefit a well-designed engine, especially if there's a card like Menagerie (or even Library or Watchtower, in a pinch) to counter-balance the discard effect.
Actually, pretty much all the cards are really nice engine enablers, especially in decks where you build up a bit of variety in the cards (or in the case of Field and Showman, some deck inspection to set them up). If my main criterion is "Would adding this card to a Kingdom make it more interesting to play?" then I think all of these succeed because I'd consider buying just about all of them, but not in a Rebuild kind of "if you don't buy this you lose" way.