At the moment Air China are the cheapest followed by Korean, Asiana and ANA. Obviously prices will vary over the course of the year and business class fares have big enough margins to allow for deep discounts.
Connection times with the above are longer on at least one of the legs, but you could have a stopover or a few hours in bed in the transit hotel. Air China would be about GBP2500 cheaper than Qantas.
It comes down to preferences, if you are happy with a B grade business class at a considerable saving then Air China would be worth looking at, however Asiana and ANA are both Skytrax 5* and only marginally more expensive.
Draw up a short list of suitable airlines based on reviews, suitability of connections and FF miles usage/accrual, then take the best price.
My preference would be Qatar but ANA come up GBP1500 cheaper in total and that would swing it for me.