Having played 1000 Goko DA games, I know for now it is not my favorite expansion. But, I feel that is because I still don't fully grasp some of the cards.
For me, Hinterlands is my favorite. I feel it offers a bit of everything.
Seaside would be my second favorite. I think it is a bit broken, but I feel that Duration cards offer something important to Dominion.
Prosperity is third, but I am not in love with it like some other players here. I feel it is the most unbalanced set in all of Dominion, but KC engines are so darn fun. To be honest though, I mostly like Prosperity for KC and Bank and to a lesser extent Goons. I am indifferent to Colonies. I don't hate them. I don't like them either. They are just there for me. And, yes, I very much realize how they change the strategy of the game.
DA is fourth. DA offers a lot of cards, but man, some of the interactions can get pretty complex. I guess this is a good thing in a way. But, there are many cards I really like such as the Shelters, Knights, Counterfit, Cultist, Spoils, etc. But, man, Rebuild is my least favorite card of all-time at the moment.
Intrigue is fourth. It has some duds like Scouts, but it is not overly broken like Cornucopia or Prosperity. Overall, it has a lot of solid cards, but no amazing cards like HoP or KC
Cornucopia is fifth-HoP is my favorite card, but I feel Tournament is very unbalanced and Hunting Party is a bit overpowered as well.
Alchemy is sixth. I don't have much to say. I like almost every card from Alchemy, and I like how Potions make you weigh whether or not to pursue that card.
Base is seventh.