He grew up among the sons of FŽanor, he palled around with Gil-galad and Cirdan, he married Galadriel's daughter, and anyone who's anyone in the Third Age passed through Rivendell at one point or another. As Tolkien says in The Hobbit "He comes into many tales", and in FOTR Tolkien describes him as "Elrond, of whom so many tales spoke".
Tales of crop failure would chill you to the bone! Actually I went for Bombadil. Too hard to choose really but I think it comes down to Elves, Wizards and whatever Tom is. Green man? Demi God? It's always been a point of interest to me that he barely gave a darn about the ring. Although I'd love to know what all Treebeard has seen I think Tom was around before he came into existence.
Saruman for the dark and chilling stories, Gandalf for the questing stories, Galadriel for the romantic and passionate ..oh, i mean the valorous stories, Glorfindel for the intense battle stories, Elrond for the educative stories, Bilbo for the fun and adventurous stories. -Need for a break-
I choose Bilbo because I think the teller would have to be in awe of what they've heard, seen, or experienced to really give the story/stories that enthralling delivery that captures the imagination of their audience. Sam always spoke of Bilbo's tales and how they wow'd him all his life. I know other have experience so much more or different thatn our Old Hobbit, but I'd still love to sit by the fire on a rainy night and listen to him :)
Bombadil has my second vote. His stories are full of lessons, not just events. His stories for the hobbits when they stayed with him did so much to prepare them for the outside world.
I don't think Eru would be telling fireside stories... :D
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And even if he did, it'd be something too much for a mere mortal like me to hear.
However, Gandalf, Aragorn, Pallando and Alatar would probably have interesting stories to hear. Reason: they're all travellers who's seen lands far and wide, and met all kind of strange creatures. Pallando and Alatar especially could tell stories of the East, of which others know not.