I recently flow MEL-BWN-MNL on Royal Brunei.
Excellent service, food and overall experience. The TV is not AVOD, but does have enough channels to keep you interested, although with small screens. Planes were clean and seats were comfortable.
Downside - 3hr layover in BWN each way with nothing really to do. Saved me $500, so was worth it. I would/will do it again.
If going MEL-LHR I think it would have to be a lot bigger saving as the two stops would by a bit more annoying, as well as the longer distance and the inferior entertainment don't really make up for the saving.
I have never flown Qatar, so can't comment. But worth looking at all the asian airlines to get the best deal as they are all fighting for your dollar and have specials at different times.