All of them were super different and fun to experience honestly. Dawnguard was really fun for me because I genuinely liked the vampire girl. I just didn't like that you could constantly contract vampirism if you fought against them. I've contracted it over 5 times now. I wish the expansion had a bit more story-I felt it was really short. I haven't come close to finishing Dragonborn so I'll comment when I have. Lastly, Hearthfire was good because obviously you can build your own place (takes ages to finish) and have a family. Although I hate the constantly spawning bandits and giants attacking my poor cow.