There are two I absolutely detest, the Knights pile (for both their main action and their extreme variety making especially Anna and Michael really really strong sometimes) and Rebuild for completely controlling the game. I cannot stress over how boring I find Rebuild as a card, even though it needs strategy. I hate the Knights much much more though.
Then there are a couple I don't like, Tournament and Black Markey for variety, curses that work especially sloggy (Sea Hag in particular, but Familiar comes a close second), Kings Court for the reason that almost every KC game is a game about who can either play KC+X or KC-KC-X first. Possession because it's just a troll, Treasure Map because it can help people without many skill so much.
And I don't like Gardens. I really, really, really don't like Gardens. Silk Roads, Dukes, Vineyards, at least you need a decent plan for them (although Silk Road can turn into a rush very much.) But I hate Gardens rushes or slogs for some reason. Contraband is another card I don't really like, but it's rather easy to play around it, contrary to most of the other named cards. Most of the universally hated cards are either very strong (gamebreaking strong in some cases) or a certain winner in certain types of games.