As many of you have already touched on, I think Mclaren and Ferrari's form will be the main factor as to who brings this home. If Mclaren end up faster than the red bulls, I think Brawn will just hang on, if the red bulls can stay ahead of the mclarens, then Brawn wont stand a chance. Then it comes down to which Red Bull Driver, well as a patriotic Australia, obviously Mark Webber would be my preference, but Vettel is a prodigious talent. I think Mark's 4 point lead of Vettel right now is crucial, and I'd bank on Mark getting preferential treatment should he come out of the next race much further ahead.
I have noticed a lot of press and people on forums seem to automatically assume Vettel is out right faster than Webber, but from all the live timing and race's I've watched there really hasnt been much in it, yes Vettel has qualified better, but the majority of those performances weren't as clear cut as people tend to suggest/assume - The first few were due to lesser fuel loads, and on the occasions where they were equal Webber has encountered traffic or made a driver error. I am by no means saying that Vettel has ended up in front by luck, but him and Webber have been a lot closer than some may like to believe, just have a look at the practive/qual1&2 and race lap times.
Anyways, sorry for the essay, I am a first time poster so had a lot to say

I look forward to talking F1 with you all from here on!