Since it's not a completed series who knows if that will continue.
Best series: Foundation.
Best Prequel: The Hobbit.
Best first book of a series: Rendezvous With Rama
Best second book of a series: Speaker for the Dead
Best third book of a series: Hero of the Ages.
Best fourth book: Clear and Present Danger.
Best fifth book: The High King.
Best 1014th book: A Memory of Light (finally).