Whichever airline you decide make sure they have flat-bed seats in Business class. Last time I flew Emirates LHR-DXB-SIN-MEL I was in First and the seats only reclined about 45 degrees, could have changed.
Family member recently came out on Virgin via HKG and SYD in Upper Class, Virgin Blue SYD-MEL and said it was competative and great.
Personally I would go SIA or QF.