What status are you with? If P1/WP, the QF F SYD one is the plushest.
I have not as yet tried the QF F lounge at SYD, have tried the J lounge though, not bad, but with nothing to compare with, everything is "not bad".
If the flight is a QF flight, can you use the EK lounge? You can certainly use the EK lounge at SYD, if the flight is an EK SYD-DXB-JHB, then sure, the EK lounge is yours to use.