Interesting question.
I guess in a way things are limited - in that the operation doesn't have multiple types and a large O/S network BUT
On the other hand - and I assume that you are a pilot - we don 't have second officers, we don't have a system that is as formal as QF, we don't have a list of pilots that is rather long - which means that promotion is based on how many numbers are above you..
BOTH QF and DJ are probably as secure as each other for pilots - which is saying something for aviation!
It depends on what you want out of life I suppose. Joining QF now is going to see you at the bottom of a long list, and things are starting to slow down. This means that promotion prospects are going to slow down. A slow down of promotion prospects means by extension that you may spend longer than others have as a second officer or a first officer - some older PUITS may never see a command in their career due to this.
You probably can't look at people in the system at the moment and judge your promotion prospects on their progress through the system.
That being said, they are paid better than the Virgin troops at the moment.
In Virgin the possibility exists for a reasonably quick command, the route structure is expanding, but you probably will never see Paris or Rome on a Virgin overnight. You probably will never also fly the jumbo or the A380. And you probably will not reach the current salary levels of the AF guys/gals.
BUT if you are of the opinion that the grass is greener - you should stick your application in and see how you go - you don't have to make a decision until they offer you a job.
REMEMBER the grass isn't necessarily greener on the other side of the fence.