I have flown down under a few times and the best is probably Cathay Pacific. Air New Zealand has the best leg room but getting to OZ would require two stop overs I think. Also wouldn't hesitate going with Virgin Atlantic who have a sale on right now.
Cathay Pacific in economy has new seats that don't recline but the cushion slides in the same way as a recline which basically means when the passenger in front reclines- you don't lose your legspace- brilliant!! Virgin has more legroom than British Airways in economy and both Cathay and Virgin have better In flight entertainment that BA.
If you are going Premium Economy, don't bother with BA it is just extra legroom and first choice of the economy meals not worth the extra.
Business- again Cathay is best but Virgin has the onboard bar

and the crew are more fun.