Hm. See, you could go in two directions with 'The Hobbit': you could go with a subtle retelling, highlighting character development and interaction, focusing on the Thorin's story et cetera, only bringing out the loud bangs and the heavy-duty special effects for the finales. In that case, I would suggest Shane Carruth, writer/actor/director of 'Primer'.
Or you could go with a very effects heavy, action-oriented telling of the story, in which case, I'd... hm... I dunno, Blomkamp? Abrams? Somebody who does action well, without completely overriding the dialog with the bangs and the flashes.
Ultimately, I'd have to say that you should get somebody who has a developed sense of style, a flair for action when necessary, and yet at the same time is capable of those subtle touches that really make a film stand out... say Christopher Nolan.
As for the poll suggestions:
Lynch? No. The Hobbit is a fairly straight-forward adventure story, and wouldn't handle the psychological loading that he would try to force into it.
Burton? GOD no, unless you were really wanting to see Johnny Depp and Helena Bonham Carter jammed into some bizzaro, super-surrealistic Middle Earth.
Spielberg? No. There was a time where I would've trusted him to handle just a straight-up adventure story, but nowadays, it seems like he feels compelled to cram some kind of message into everything he does.
Anderson? I suppose that could work, but I was never as impressed with Bottle Rocket as everyone else seemed to be.
Cameron? I don't think this would work, if only because he's gotten so successful, he wouldn't accept being 'merely' the director. He would want to imprint his 'vision' on every part of the film(s), and I doubt very seriously that Peter Jackson would allow that, considering how unpredictable the outcome would be.