I'm going for Australia, although Haydos and Gilly have never really done much in 20/20 there is always time, plus they are so strond down the order with players like Punter, Mr Cricket, Simmo, Pup, ect.
My only concern is the bowling, but if Binga can start bowling 95mph yorkers at the end then he could be a handful, Mitch Johnson seems to have more control, and Stuart Clark is fairly reliable.
But 20/20 is more of a lottery than any other form of cricket and I think it will be settled more on the day than anything else.