Blood & Wine and it's not even close. That DLC had more content that a lot of single-player games. For example, I'm 100% sure that B&W has more content than The Last of Us. And this isn't just about quantity, the content in B&W is still really good. The fact that a DLC can have more content than a full AAA game and this content still has good quality astonishes me. Easily the best DLC ever.