I think Azarenka deserves to be called the favourite at this point. It's easy to forget just how good she looked on hardcourts at the beginning of the year. Even though her US Open record looks bad on paper, I wouldn't read too much into that - she has got relatively unlucky there (the fainting in 2010, drawing Serena early last year - the only real head-scratcher is her loss to Schiavone in '09).
Clijsters if she can even refind the form she had at the Australian Open this year, will be very tough to beat in New York which suits her game to a tee. I have to admit though that her play on grass has got me really doubtful - hopefully though, as the USO will be her last tournament, she'll be willing to throw off the shackles and move at full-pelt and risk some injuries (as they won't really matter seeing as she'll never be playing again after that anyway), and with the crowd behind her more than ever, it's conceivable that she could go all the way one last time.
Serena, obviously a possibility, but pretty unlikely. Her serve just isn't going to be rewarded quite as much as on grass, and let's face it, her ground game really didn't look great at any point this tournament. I'm not sure I really buy the argument that her mental problems will have gone because the "pressure" will be off just because of today's win - that's typically not how it works with players who've past 30, they typically just get more and more headcasey with every year that passes.
I really do have a good feeling about Sharapova's chances - I really don't accept the argument that she's only suited to slow courts - grass is a different issue because of the low bounce which she just hasn't been able to get down well enough for ever since 2006, but I don't think quickness
of a surface is an issue for her as long as it bounces high enough like at the US Open. The wind is a more relevant issue for her I think, but there's been encouraging signs that her serve is holding up well in wind this year, esp at RG. With that said, I understand her piss-poor recent record at the USO will stop her from being seen as THE favourite by many people, but personally I think she's got a pretty good shot.
Although I've been tirelessly battling the TF belief that Kvitova will never amount to anything on "American hardcourts", she's clearly not going to go all the way THIS YEAR if she couldn't do it on grass. Hopefully just a QF there and some more solid results this season to give her some sense of confidence going into the offseason, when she can start working hard and maybe finally start fulfilling her potential (on hardcourts and grass) next year.
Stosur.... I have no idea anymore. I don't necessarily buy into the idea that she's a claycourt specialist and that her US Open title was a complete fluke, because I do think the courts there are a fairly good fit for her (it's not really the speed of the surface that matters with Stosur, it's the bounce - the Australian Open, even though it's slower than the USO, has a lower bounce and doesn't receieve the spin from her forehand as well as the USO does), but mentally I still haven't really figured her out. I don't necessarily agree with the predictions that she's going to flame out early, but equally it's hard to see her going all the way, as for that happen she would need to avoid her many nightmare match-ups and/or produce a performance as utterly inspired as in the final last year, which seems fairly unlikely.
She seems mentally to have no belief left whatsoever. The Australian Open is probably her only chance of ever getting another Slam final/win, it's not happening here.
For me, I think this "streak" of different champions will be broken because it's really hard to see a winner outside of that 7 (or, rather, out of the 5, with Stosur and Li not really included), but, this is the WTA, so....