What an awesome feature! Thanks to the team for making this possible. I think my favorite part of these lists might be hearing players' explanations for why they like/dislike/ban certain cards. Should make for some great conversation. Having said that, here I go (for now)
Like: I don't have anything on this list because I enjoy the variety and challenge of giving (almost) every card a chance to shine. If I did have cards on this list, I don't know how I could possibly limit it to 5. My instinct is to put Worker's Village just so there's always a source of +actions and +buys, but I prefer the randomness of it all. I might also think about putting Black Market on here, but having it show up more often than usual would probably wear it out and lead to increase swinginess.
Dislikes: These are the cards I could do without, but I wouldn't say that I "never" want to see them again. They belong in Dominion from time to time and I'm glad that they get their occasional chance to shine.
Familiar- It just leads to sloggy and uncomfortable games. You have to dedicate your first 2 turns to hitting $3P, and if you don't hit it on turns 4 and 5, you're probably hosed. Before you know it, you're most likely sitting there with 7 coppers, 3 estates, a potion, a couple silvers, and a bunch of curses.
Pooka- I don't like Cursed Gold. That's all there is to it. I wish it wasn't in the game. I do like Pooka, though. That's what makes it a dislike rather than a ban.
Urchin- I find that it's often a race to get Mercenary and then a money-ish situation after that. I also feel like it's usually the best thing to open urchin/urchin and I'm just not all that excited about that.
Swindler- It's the swinginess. It's a fun card, but one that can absolutely determine the outcome of the game on turn 3. A perfect example of a card I would like to see half as much as the others.
Smugglers- I kind of stink with this card. It's probably all in my head, but it feels like my opponent is always smuggling Golds and Goons and Grand Markets with this thing while I'm either gaining silvers or gaining nothing because my opponent bought an event or a province. However, "I'm bad at playing with it" doesn't seem like a good reason to ban a card outright.
Ban List: A very short list, but these are the cards I'm 100% sure I would be cool with never seeing again. The fact that there are only 4 card shaped things here should speak to how well I believe Dominion is balanced.
Possession- Built in already, but this card does not belong in the game for me.
Knights- The only kingdom card. I've gone into more detail on this before, but Knights take away the balance of fairness. If you have 3 Knights and I have 7, I trash all your Knights and then I'm trashing everything else of value in your deck and there is literally nothing you can do about it. Ghost Ship, Mountebank, and Cultist are nasty, but there's always the opportunity to return the favor for your opponent. Knights can and will take away that opportunity. The only true no-brainer on my personal ban list.
Tax- This is here because of the setup clause. Everything about that is gross. I've never played a game with Tax and been glad that it's there.
Keep- I mean, maybe if it was like 2VP for each treasure, but 5?!?! Holy cow it just turns Dominion into a completely different game, and one that is much less fun than the normal one. Counting silvers and buying coppers (shudders) is just a chore I could do without.
That's what I've got! I expect to see a lot Rebuild, Ambassador, Cultist, etc. on other list, but I don't really mind them as much as others do. Curious to see how my list differs/compares to the majority.