At this point in time Qantas and Cathay Pacific do not require a degree to join either company as a pilot. I could say "end of story" but I won't.
The diploma that people talk about is a glorified formalisation of the CASA exams you have to do. Remember, it's the CASA exams that count for your licence. Nothing else.
If you have to get something, get the diploma through tech.
If you really want a degree and nothing wrong with that, you can either get an aviation degree or something else. As many folk have found out in Oz, an aviation degree won't be much use unless you go into aviation. However, if !!!! happens and you lose your job or medical etc, at least you have a formal qualification IF you select another degree.
Naturally the universities have told you that airlines like degrees, of course they're going to say that. What the uni's didn't say is that the airlines like any degree. One in science/technology is more desirable than eg fine arts.
Remember that the flying schools will probably try and tell you a load of promotional rubbish too. The biggest lie at the moment is "there's a shortage of pilots coming".
Cathay and Qantas seem to look for a different sort of applicant. Cathay like you to have a well rounded aviation career with a good mix of flying. QF, I wouldn't have a clue... So, with that in mind a degree will not help you when you are knocking on the doors of the charter guys in the Kimberley. In fact, using it as a selling point will get you laughed out of the place.
Personally, a good trade is better. Electrician, mechanic etc.
If you really want to know what QF and CX prefer, contact them.
So, if you want a degree, get one. Just don't limit it to an aviation one. If you want a diploma, go to tech. (if they still run them). If you don't want either, no problem. It's the licence and the logbook that counts (and your personality). Get the best marks you can at school as this will help.
Good luck.