Confession time: I have yet to listen to the complete soundtrack of any of the movies. Part of this is due to time constraints, and the other part is that most of the pieces are so gloomy-sounding that I can't listen to them too long. (This is not to say that I don't like them--this is coming from a crazy Les Mis fan, after all. But even I have my limits.)
However, based on my limited knowledge and my end-credits-song preferences, I'm going to say that the BotFA soundtrack is actually my favorite--it has more variety in mood than the other soundtracks. I especially like "Fire and Water". The FotR soundtrack is a close second, though. My favorite piece there is "Concerning Hobbits".
Day 06: Favorite moment/line in The Two Towers
Yes! An easy one! :D I love a lot of things in TTT, but the "Po-ta-toes" exchange between Sam and Gollum (with Frodo going, "You guys...what even..." in the background :D) wins, hands-down. It's hilarious and touching and just a small bright moment in a movie that's growing steadily darker.