This is the worst part for me too. I don't know that I have a favorite, I love the books.
Tom Bombadil is an enigma, but without him the hobbits could not hope to have escaped the barrow wight. The barrow wight was necessary, because Merry received the sword of Westernesse, with spells for the bane of Mordor wound into its making, from his lair. This is the sword that he stabbed the Witch King of Angmar with, undoing his immortality and making it possible for Eowyn to slay him. The passage describing the passing of Merry's sword afterwards, is one of the most beautiful pieces of writing anywhere.