This is an amusing question in part because it's never been posed to me before. And I'm a fan of musicals from way back, having even performed in a few back in high school. I gave serious thought to which book would best translate to stage and who would do a great job with it.
I finally settled on THE MARK OF THE TALA, the first book in The Twelve Kingdoms trilogy and the overall Uncharted Realms series. I considered The Forgotten Empires books, but I think this story has an arc that would work best for stage - and I can envision the musical numbers. This entire trilogy was heavily influenced by the musical Wicked. There's even a scene in book 3, THE TALON OF THE HAWK, that I drew directly from a climactic song in that musical.
Therefore, I'd pick Stephen Schwartz for the music and lyrics and Winnie Holzman for the book. If they could do for THE MARK OF THE TALA what they did for Gregory Maguire's novel Wicked (which is an amazing book, if you've never read it), I'd be... well, I'd be defying gravity!
