The opening batsmen combination will prove the most crucial decision for Australian selectors. Vital they get it right, as the IPL and previous international games have shown that a decent opening combination is the difference between a 120 score and a 160+ score. Very difficult for teams to make a comeback from 2/20 after 4.
Any bat out of Haddin, Clarke, Hopes, Watson and Warner may be used for the position.
Watson is the most suited to open. Most likely to score a 50+ score at better than a run a ball. More adaptable than all the other candidates, is actually capable of mixing defence with ability to hit over the top.
Warner is the gamble. If he comes off, 180+ is possible. Has actually shown remarkable consistency over T20 games with Australia, NSW and in the IPL. Not always scoring a big innings, but providing a quick start.
Haddin, Clarke and Hopes all suffer from similar issues. Each batsmen can get tied down at one end early on. They all find it a struggle to pierce the in-field early, totally reliant on a big shot to get out of trouble. Which is not the natural game of any of the three batsmen. I would back Haddin and Hopes over Clarke to actually compile a decent innings.
My preferred combination is:
Watson and Warner
But depending on team selection, the combination may prove anything.