Be aware that EK J varies a fair bit between aircraft types. The A380 has a very nice J cabin, be even there half the J seats have 5 inches more leg room than the other half The DXB-MEL non-stop is operated by A380 so definitely the one to choose, while DXB-KUL-MEL and DXB-SIN-MEL use 777s and to be avoided if you have a choice. Personally I think QF A380 J is comparable to EK but different, so it boils down to minor points of difference. LHR-DXB-MEL on QF A380 would be my choice, the ground part of the service (limo/lounges) is identical and QF wines are superior to EK (not just my opinion, QF consistently wins awards for best J cellar in the sky). Service on EK can be aloof and it can be excellent, it varies by flight; overall about the same as QF in J.