Hey, we have a thread about which cards people hate, so it's only fair :)
I'm going to use this little format to classify the different kinds of awesome that a Dominion card can be, feel free to use it or not:
Best Design -- These cards are balanced and interesting. They interact in many and sometimes unexpected ways with other cards, and go up and down in value depending on what else is in the spread.
Most Fun -- Actually using these cards is a joy, even if maybe they're a little too good or not good enough.
Most Powerful Yet Underrated -- The cards that make me happy when I see them, because I'm probably going to win.
Important -- I see these as solving problems, filling holes, and generally making the game go, despite not being uniquely as awesome as the others.
So.
Best Design1.
Watchtower. I can't get over how beautiful this card is. It does so many useful things and has so many great interactions without even coming close to being overpowered (except maybe with University). AND IT LETS YOU BUY ALL THE COLONIES ON TURN 5.
2.
Steward. Imo, the perfect execution of Intrigue's 'choices' theme. A recent thread attests to how nonobvious early decisions with it can be.
3.
Tactician. Really effectively teaches the principle that one great hand is better than two good ones. Also a really interesting limited way to get 2 actions but not more. Also has ridiculous awesome combos with Golem and Black Market.
Most Fun1.
Fairgrounds. I cannot express how much I adore this card. Figuring out which four cards in a normal spread you're going to not have, getting them to 10VP with Black Market, buying that clutch Curse at the end of the game to ratchet them up for the win... Fairgrounds is just awesome.
2.
Native Village. I just really like this card! Gives unprecedented deck control, many cool combos, and an interesting decision (AND two actions!) almost every time you play it.
3.
Apprentice. I love the agonizing decision of whether it's time to start trashing your Golds, and I love deciding to throw away a guaranteed Province and being rewarded with two.
Most Powerful Yet Underrated1.
Wishing Well. I will be writing and article (hopefully soon) on this subject with copious example games that I've been collecting for a while.
2.
Scrying Pool. God damn this card is amazing, and at 2P you don't usually get screwed by Alchemy variance. You can do amazingly well buy just buying as many of them as possible and almost nothing else -- not that you can't do better by buying other things too!.
3.
Conspirator. I've read several people recently talking about how it's 'hard to make them go off' or how they can 'never get them to work'. I really don't get it. In my earlier Dominion days, I thought this card was stupidly broken and should cost 5. I don't think that anymore, but
damn it's a good 4. And with #2 and #1 on this list?
Hellooo!
Important1.
Horse Traders. A great card in it's own right, it solves the Minion problem beautifully, while providing an interesting sliding scale of usefulness against the other attacks.
2.
Chancellor. One of the two real 'wtf' moments for new players, and an ongoing source of disagreement for experienced players, this card is valuable more for the thought it provokes than the gameplay it creates, though there are certainly situations where it creates great gameplay. Also, the key ingredient in most 'perfect shuffle luck' puzzles!
3.
Lighthouse. An all-purpose attack-stopper that's actually good enough to put in your deck without being sad about it. Totally necessary in a game with attacks as good Mountebank in it.
Honorable Mentions (Things I'm sad didn't make it into any of the above):
1.
Goons. This card just does EVERYTHING! It's a little too mean, I think, and a little too good, but it's SO COOL!
2.
Horn of Plenty. I think this card might have the widest and most filled-out range of power levels depending on the spread. I've seen it be utterly worthless, not very good, a solid 5, the best 5 by a long shot, and game-breakingly combotastic. Also a really unique concept.
3.
Bishop. Plays a couple different roles, pretty polarizing in terms of community reactions, all-star in one of the coolest decks I've ever made, interesting choice of how heavily to trash estates to your opponent's bishop when waiting for your own would be 2 points better.