Ugh, please no Christopher Nolan. He doesn't have that sense of magic that is needed for Star Wars. He's too into dark and gritty for that. Likewise, Joss Whedon's style is too snarky for it.
My top picks, in order, are Steven Spielberg, Garth Jennings (the director of the Hitchhiker's Guide to the Galaxe movie), and Guillermo del Toro.
Garth Jennings may need a bit of explanation: that movie was the best example of a living, breathing alien world (universe, really) I've ever seen on film. del Toro's films are second only to H2G2 in that department. Steven Spielberg, well, he's good at getting that magical feeling that Star Wars needs. If Jim Henson were still alive, he'd also be on the list, since he did both the magic and the living world. Heck, Jim Henson studios did the creature effects for H2G2, although Henson himself had been dead for decades by the time the movie was made.