Candlestick Maker
I suppose I'll state here that coin tokens are pretty awesome. That said, I think I've been overbuying these guys a bit. They are nice for pulling yourself out of a slog or for saving up alongside an aggressive early-game trasher such as Chapel, Mint, or Doctor. And of course, one or two are often welcome simply for the nonterminal buy.
Stonemason
The on-buy is pretty awesome, especially in an engine. As for the on-play, it isn't all that bad as a Copper/Curse/Ruins trasher since you are often buying it anyway to double up on engine pieces (so the opportunity cost isn't as steep). Apart from Copper/Curse/Ruins, I found myself most often targeting Gold. As I'll mention later, the Gold from Soothsayer was threatening to clog my engine until I began turning the Golds into pairs of engine pieces!
Doctor
A very fast early game trasher, but rather weak later. More than any other card, Doctor breaks the symmetry between your first two hands (much stronger on 5/2 than 2/5). Doctor is able to trash down your deck nearly as quickly as Mint or Chapel unless you are quite unlucky with your first couple of namings. It does give you enough time to build up a bit of economy before your Coppers vanish, as opposed to opening Mint. Later in the game, however, it becomes a much weaker trasher, particularly for handling Curses/Ruins or activating on-trash. Its best use later seemed to be for peeking at and rearranging the top of my deck.
Masterpiece
I like this card a lot. It appears to be a very potent Silver-flooder when you have some decent drawing power available like Smithy. Taxman can trash the Masterpiece and topdeck a Gold.
Advisor
Ugh, this card reminds me of Spy with how much it can slow down a game while contributing so little. I frequently had to choose between discarding their Silver or another Advisor. I often discarded Silver, but I think that was wrong; those Coppers they picked up more than made up for it, and they got a lot of cycling.
Herald
I kept trying to get this to work, but it seemed to be as fragile as I feared. It needs a board with 1) good trashing, 2) no junking or manageable junking, and 3) a reason for spending your $4 hands on Heralds rather than other engine pieces. I haven't explored the on-buy effect much. It gets pricy pretty fast!
Plaza
Not bad. You are often willing to pay $4 for a vanilla village anyhow. I had a cute game that involved playing several Merchant Guilds, buying three Coppers, and then next turn drawing my deck, discarding the Coppers to Plaza for coin tokens, trashing them with Doctor, and then buying three more with Merchant Guilds in play.
Taxman
A nice opener for attacking while transitioning Copper into Silver. In the late game you can get some nice smoothing by trashing a treasure you don't need and topdecking an even better one for your next hand. Contrast to Mine, which is generally only good early in the game since it's just a terminal Copper at the end.
Baker
The opening coin token is fun. As for the card, it's petty nice. Sure, there is often a more crucial $5 on the board, but those cards are often terminal. After buying a Soothsayer or two, you are ready to start spending $5s on Baker.
Butcher
$5 is expensive. I haven't really found this card so attractive yet. When I did get it, I mostly turned Curses into Copper while saving the two coin tokens. He's like a reverse Swindler. A Reldniws?
Journeyman
Decent drawer. Not much more to say, except that I often struggle to decide which card to name.
Merchant Guild
I had some fun going for Merchant Guild megaturns, but not being able to spend your coin tokens that turn is a real buzzkill. Even if you save up a couple dozen coin tokens, there's something anticlimactic about piling up an additional twenty off the four Provinces you buy, but without ever being able to use them. Anyhow, this is definitely no Goons. Goons turns can take a long time to build up, but you have a few advantages: 1) The Goons attacks, slowing your opponent, 2) you don't touch the Province pile, so your opponent needs to buy all 8 Provinces, 3) you end the game in one big megaturn, rather than needing effectively two consecutive megaturns (a tall order if you just bought 20 Coppers during the first megaturn!).
Soothsayer
I didn't expect the Golds to clog up my engine so much! On the other hand, the Gold are really nice if you have some sort of trash for benefit card like Remodel, Salvager, or Stonemason.