When you played PSIII, which quest did you enjoy more, Ayn's or Nial's? They're both pretty unique, compared to all the other quests, and have a nice variety of characters.
Personally, I prefer Ayn's trip. It is the only part of the game where we get to see the consequences one of the marriage decisions had on areas other than where Rhys, Ayn, etc. chose to live. I liked returning to Landen to get Sari, then going to explore the other dome to rescue Thea.