People, may I just butt in for a second with a few words of advice.
I was a military pilot for 22 years, mainly RAAF but about 5 years working with and then in the Army.
I'm not familiar with the details of changing between services in the current training world prior to wings, but would highly recommend taking whichever you can get.
Naturally most people will have a preference, and you should go for it strongly, but be aware that the training you will recieve is very good in all three.
As has been said, the RAAF and RAN get different training to the Army, and to my mind the PC-9 route is a good grounding for any flying you are likely to do later. It is also the de-facto standard for service transfers as a qualified pilot - people trying to go from the Army to the others need to do a 'validation' course at CFS to give them those elements of training that they would have missed in their own basic training, such as high/lo nav and combat form. However, such transfers can and do happen.
Also, I'm not saying the Army training is substandard, just different. Many RAAF pilots would be keen to fly helicopters, and some cross-service postings have happened recently. Of course the RAN is basically helos too.
This is probably a bit off track for you guys, but what I'm getting at is that if you can get yourself into any of the services for a pilots' course, do it. No matter what type you fly in what service, you'll get professional training and satisfying operational flying, and if you decide to pull the pin later on you will have a log book full of good experience that would cost your civil counterparts more than anyone can afford.
Best of luck.