Had to go with Contraband. $3 with a Buy is pretty good, but goddamn does the contraband itself hurt. Thief, Transmute, and Chancellor were all other contenders.
I really have a liking for Secret Chamber. I love setting up the top of my deck for Swindlers, Jesters, Knights, NB, etc. Even with Ghost Ship, it gives you a little more choice.
Moat: dat defense, though. It's great to be sitting pretty on that.
I've been in situations where I've really appreciated the cheapness of Duchess as a terminal Silver, so I have trouble calling it the worst.
Develop has that favorite thing of mine in Dominion, the potential for really creative play (why Count is one of my all-time favorite cards). It really good in engines where you're practically gaining the cards in hand.
When it comes to top-deck play, sure there's Apothecary, Cartographer, and Wandering Minstrel, which are all better, but you know...sometimes I REALLY want to know what's on top of my deck. If there's a combo potential with Mystic or Wishing Well, I'll probably throw Scout into the mix.
Counting House can be the center of a full-game strategy. Even though it needs support, it's hard to call it the worst for that reason.
Explorer: yeah, I wouldn't really consider this one. I like Silver. I like it in my hand best. Nuff said.
Finally, especially with some good trashing like Loan, you could definitely do worse than Adventurer when it comes to Big Money.