Kudos to the original poster for coming up with a good shortlist. Took me a while deciding on my final 4 (and I'm still not sure about it!).
I voted for Brad Bird first off and without hesitation. Great sense of spectacle and humour and is good with character dynamics. I would totally squeal like a girl if he was to do it.
I also voted for Neil Blomkamp solely on the strength of the amazing District 9. Like Lucas, I think he'd have no problem coming from doing a more gritty and adult-orientated sci-fi movie (like THX-1138) into a poplulist crowd-pleaser. And Sharlto Copley as a scuzzy alien lowlife? Yes please.
Duncan Jones with the keys and budget for something like Star Wars? Hell yes. As long as he doesn't cast his dad in it.
Final vote, possibly a little too subjective, having seen Skyfall a few days ago, was for Sam Mendes. It would be something new for him. But he proudly boasts that there is no such adjective as 'Mendesian' and I think he'd have no difficulty in tailoring his style for something like a SW movie.
Others I'd like to see would include Spielberg (who I've been hoping would make a SW movie since I first read in 1985 or so that he was going to make one) and Joe Johnson, who largely replicated the fun of Raiders with Captain America and who I think could do something similar with a SW movie (but replicating SW, rather than ROTLA). Kenneth Branagh might also do something interesting with it.
I'd have no problem with either Joss Whedon or JJ Abrams making a SW movie - but I'm quite happy with them to remain at the helms of The Avengers and Star Trek franchises respectively.