Alagaësia seems more understood than either of the other worlds, with Narnia conjuring some new random magic every book and Middle Earth full of mysteries, but I think I like Middle Earth more due to the deep lore it has. It stretches back all the way to the creation of the universe. I then put Alagaësia as a close second, and Narnia as a far inferior third.
I think a perfect medium would be a blend of both the worlds of Alegasia, and Middle Earth. I personally like how the female Dwarves in Alegasia don't have beards. I could probably outline the blendings I have in mind, but I'm not so sure I should.