Jetstar is hardly much different to Qantas - it would make so much more sense to fly to Singapore and then fly down to Darwin from there rather than fly 8 hours to Sydney and then 4 hours to Darwin

Book row 1 on Jetstar and I would rate it better choice than economy on Qantas. The only thing that they are really missing is lounge access and that can be purchased at lounges in Singapore if they want to - Save the 3800 miles detour