I just did Austrailia-Japan-Australia with my family. Northbound sector was with Jetstar and we came home on QF 22 with Qantas. Overall, each product was satisfactory with the following observations:
Jetstar.
A330 aircraft. New and smelled nice. Crew were mostly foreigners based in Singapore. The Purser/Cabin leader was an Aussie girl about 25 years old and did at no stage look or sound comfortable with what she was doing. We had pre-paid for meals and got a standard airline economy class slop in a plastic tray followed by a 'vegetable curry roll' later in flight. After meals were provided, the cabin crew all managed to make themselves totally invisible except for a couple of forays into the cabin to sell duty-free items. Having said that, all interaction with CC found them to be cheery and friendly. PA from the FO sounded like he he could probably read and write as well as talk.
Of note that when we had checked in for the flight to Japan, J* staff told us that the airline had been trying to contact us to tell us that we had been re-booked to depart in another 2 days. We said that we had not heard from them and that this would be a huge inconvenience. A supervisor arrived and determined that no emails had been sent and that there was a note to say that when Jetstar had called, they didn't leave a message and would try call us again later, which they didn't do. The supervisor made some calls to a higher up and pointed out that the airline had failed to inform us of the change. After some firm argument from her, she managed to convince whoever she was talking to that we should travel which we did. We thank her for her efforts and professionalism.
Qantas. (Southbound).
Old B744 aircraft. Interior was clean but the interior was so dated, that the signage was written in hieroglyphics. Cabin crew could only be described in these terms: professional, friendly, slick, confidence inspiring. Captain made the usual PAs and sounded like an articulate industry veteran. It was a great relief that he could provide flight details and avoid the dull and hackneyed "sit back, relax and enjoy the flight" (which makes me cringe every time that I hear it).
Economy class food was not the Rockpool level, but was ok. I didn't eat the white suff with yellow fruity looking thing on the top that was apparently 'dessert' but the Roast Pork main was fine as was the Sav Blanc served by the friendly and helpful CC named John. In-flight entertainment was not as user friendly as on Virgin B777 and had less movies but was ok. Drinks were served at regular intervals and we were happy.
The price for each sector was pretty much the same, Southbound with QF a little cheaper. In their own way, the product by each carrier was fine.