Dair>>>>>Chair
I know a lot of people adore Chuck and Blair, and despise Dan and Blair. But honestly I prefer Dair by a long shot. Now I fully believe in unconditional love, which could be argued is what Chuck and Blair have. But I also believe that there is a line that when crossed, the relationship should end. This is a line I feel Chuck has crossed on multiple occasions, from giving Blair to get his hotel back, to sleeping with her nemesis, to almost hitting her when Louis proposed to her, and managing to cut her face. While Dan did cheat on her with Serena at the end of season 5, but everything during their relationship was so fun to watch, and it wasn't toxic like Chuck and Blair. A lot of people say that Chuck changed when he was with Blair, but honestly I saw him to be the same person, just not a rapist, which he only was in episode 1. He's still manipulative and immature, just like Blair was when they were together. When Blair was with Dan, it was what a relationship should be(aside from cheating obviously). Blair was easily the nicest she's ever been when she was with him, and they always brought the best versions of themselves when they were with each other.