There are 6 cards that has "several" votes. Only 2 of them are imo reasonable choices.
Duchess - Are you kiding? Duchess is for free! Also it could be great as a starter if you have 2/5 split and need some extra money to keep up. It is a bad card, but it is so cheap you cannot bitching about that!
Develop - Grand Market. Border Village. Ill-Gotten Gains. Anything that costs 7$. Gardens (trashing later your parts to Gardens-something). Silk Road (trashing later to Silk Road-Estate). I probably even forgot lots of things...it is a bad card, but it has some situations where it is VERY good and they are not so rare (you really need just one of these cards.
Adventurer - Without other strong terminals on board, Adventurer is good. When you have e.g. Gold, Gold, Silver, Silver and 7 Coppers - Adventurer is stronger than Gold. That is of course still bad, but not worse!
Scout - This is just wrong! Minion, Vault/Secret Chamber, Wishing Well, Scrying Pool, Tactician and many more!!! And of course - Crossroads+Scout. That is one of my favourite combos. Sure, it needs something other to cooperate, but then it is awesome:
http://councilroom.com/game?game_id=game-20120207-123440-03e8a7bc.htmlhttp://councilroom.com/game?game_id=game-20111224-161140-0ecc49e9.htmlSo here comes the 2 only reasonable cards: Thief and Transmute. I choose Transmute, for these reasons:
1. Thief defeats BMU.
2. Thief is at least ok on boring boards with 4+ players.
3. I cannot think of any non-obscure situation, where Transmute would make any difference.
4. Thief is at least good when you are starting with Dominion.
Stats are not very accurate here - when you are behind it is good idea to buy Thief and hope you will be lucky to steal some Golds, which lowers the winrate. And as for Transmute - many times there is something juicy with Potion in cost on board and you pick Transmute rather than buying nothing...and by this lowering your chance to win by 0.1%.