Disclaimer: Dominion does a really great job of balancing its Kingdom cards. Pretty much every card has some situations where it shines, and some situations where it doesn’t. Nevertheless, some cards just end up being flat-out better than others, either because they are more useful more often, or just ridiculously good when they are useful. Don’t expect this list to be very scientific.
Honorable Mention: Harem
In many ways Harem is similar to Nobles, but Harem is on this list and Nobles on the Worst list because it doesn’t really need any additional support to make it worthwhile. Without support, Harem is much better than Nobles even if you’re using the Nobles for the +3 Cards: unless you have +Actions, or you’re running a pure Big Money deck, Smithies are generally worse than Silvers!
At the same time, Harem benefits just as much from support as Nobles does: it stacks wonderfully with Hoard and is a great Mint and Mine target.
As noted before, you should start taking Harem over Gold around when you would start taking Province over Gold. It’s a little weaker against attacks than Gold, but especially in games without +Buy and good draw, the coin difference doesn’t make much difference, and the 2VP adds up to quite a bit.
This is a bit of a cheat, since you would rarely actually buy Peddler at $6 or more. And it loses serious points in games without any +Buy, since you’ll rarely want to buy this with $8 in hand, even if it’s free. It might be useful in very-low-money no-Buy Curse-infested games, where you might actually play two or three Actions but not hit $5-6, but otherwise Peddler is usually not worth spending your whole Buy on.
But it’s a glorious card when you’ve actually got the +Buy: traditional Market-type decks depend on density, and so the usual way to make it work was to trash everything that wasn’t a Market. Peddler works the opposite way: achieving density by filling you up with so many Peddlers at once that it doesn’t matter that you have junk in your deck. (Conditioned, of course, on you having enough +Buy to make it worthwhile.)
The real reason Peddler is such an all-star, though, is how it interacts with all the cost-based Actions. Remake them into Platina, two at a time; Salvage them for +$8; Bishop them for 4VP; Apprentice them for +1 Action and +8 cards. They’re even great defenses against Swindlers, since if the Peddlers are exhausted your opponent will hesitate to play Swindlers for fear of converting your Peddlers into Provinces.
On the worst list, yes, but Hoard is also on the best list, primarily because it’s such a strong card in Province games that you can’t ignore it. It’s one of those rare almost-must-buy cards even without its support: in a vanilla Province game, you can get all the Golds you need just from Hoard. By the time you should stop buying Hoards with $6, you should probably be buying Duchies instead.
Plus, it has all sorts of hidden synergies that you might not immediately expect. Salvager / Hoard is a great way to deal with the Duchies and Estates you accumulate with Hoard, and gives you the +Buy to extract maximum benefit out of the Hoard; Apprentice lets you use your Duchies for the +Cards needed to draw all your Golds; even the lowly Trade Route synergizes with Hoard, since all those Victory card buys free up Trade Route tokens and send it to +$3.
And I haven’t even mentioned its delicious interaction with Kingdom Victory cards.
Goons needs no introduction. Its appeal is immediate and obvious: no one really forgets that first game they got crushed by Goons. Before Goons, it was inconceivable to score over 60 or so in a 2-player game; but with a big Goons stack, scoring hundreds of points is almost trivial. Because you’re not interested in buying green cards, there’s simply no way that someone rushing for Provinces or Colonies can beat your Goons stack, since every purchase they make slows their engine, while every purchase you make only further accelerates your engine.
But Goons falls to #3 on this list because it is heavily dependent on a supporting engine. Big Money + Goons is hardly any better than Big Money + Militia; in order to really deploy the Goons stack, you need enough +Actions to play all your Goons, you need +Cards to draw all your Goons, and you need to be able to do this consistently on a 3-card hand because your opponent will probably be Gooning you just as much.
With the right setup, Goons is an unstoppable juggernaut. Without that support, Goons is a nice kicker at best.
2. Grand Market
The mark of a good Kingdom card is when you’d take it over Gold. The mark of a truly obscene Kingdom card is when you’d seriously consider taking it over Platinum. Grand Market falls into the latter category: the +$2 instead of Market’s +$1 is an insane boost over Market. It makes it even easier to get more Grand Markets, and it makes it probably the single best target for a Throne Room or King’s Court, since Grand Market literally gives you everything: Actions, Cards, Coin, and Buys.
Grand Market just edges ahead of Goons because it’s a worthy addition to every deck, even if it can’t score quite as obscenely. Grand Market doesn’t need any support: it’s just a free +$2 and buy on every turn. No deck is ever hurt by the addition of a few Grand Markets: it is one of the few exceptions to the general rule that you should avoid delaying Province or Colony buys for Kingdom cards. I am happy to go second in the Colony race if it means I get an extra two Grand Markets in my deck.
1. King’s Court
Raise your hand if you accurately predicted that the difference between Throne Room and King’s Court would be this staggering. Then put it back down, because you didn’t. In playtesting, the card was originally priced at $5, which might have seemed intuitive at the time but in retrospect “did not turn out to be [a] good guess“.
Throne Room makes for merely cute plays; King’s Court leads to truly obscene plays. You can make your Coppers worth $10 each; you can grind your opponent down to a 0-card deck every turn. The fact that King’s Court works so much better on itself than Throne Room does is the icing on the cake; there’s nothing quite as thrilling (or ominous, or groan-inducing, depending on your viewpoint) as watching someone announce a King’s Court on another King’s Court. Virtually every single ridiculously lopsided game in Dominion involves this card in one way or another. Much as Menagerie is a defining card of Cornucopia, so too is King’s Court the defining card of Prosperity.