Probably Avatar based on the Golden Globes.
For a long while The Hurt Locker looked the front runner (and would be my choice) but Avatar = a plot Hollywood clearly likes historically, a huge success (Hollywood likes that too) and has shown big 3D movies can work (which Hollywood is keen on because it reckons you'll pay more to see them and be less likely to pirate them).
So pat on the back for Avatar probably.
However, like I say having seen all those films I'd say The Hurt Locker was the genuine best film there, followed by Basterds and Up In the Air.
Try to be reasonable... its easier than you think...