I just put together a top ten, and I guess I'm a sucker for theme. Which is funny, because theme is something Dominion is notoriously lacking. Still, when a card's function and name and art come together, I guess I dig it.
Honorable mention: Jack of All Trades - Great card, with great art to boot. Just look at that guy. Such a pimp. He's like "'Sup. I'm adequate."
10. Possession - Captures the card's purpose perfectly.
9. Tactician - Love that it looks like the dude is facepalming.
8. Witch - Still strikes fear, just looking at her.
7. Border Village - That's an epic-looking village. Fits.
6. Stash - Almost photorealistic. (I think it sort of is, SdJ judges and all.)
5. Watchtower - The blue Reaction border accentuates the wintery theme. Looks good.
4. Noble Brigand - Even more badass than the Jack. I'm taking your Gold, sucka.
3. Hunting Party - I'd love to see this full size, you can tell there's tons of detail.
2. Trusty Steed - How could this not be your first Prize pick?
1. Ill-Gotten Gains - Those gains? Those gains are trouble.
Seems I agree that Hinterlands has the best art. Although maybe it's just because it's still new?
Worst single card art-wise is a toss up between Navigator and Tournament. I like Harem, man. Woman, even. It's different, but it's got style. It's like Wind Waker. Navigator and Tournament though. Yeesh. They look like something I'd draw.
And that is not a compliment.