Taking the flight to SYD means that you avoid TBIT and have lots of flights to MEL if you are late.
The longer flight would be a plus to me for the SYD flight as you can sleep more. I took the AKL flight before and found it is harder to get over jetlag because of the very very early arrival time.
I'd disagree with Dave and say avoid QF8, but then again, I can think of nothing better to do than sleep when in WHY for 14 hours.