Firstly, what trade are you applying for?
I'm Currently trying to fight the idea of Pilot out of my head. It's my "childhood dream" job but the odds of getting it are so distant (at least I assume they are) that I'm going to concentrate my efforts elsewhere.
Otherwise I'm currently torn between Weapon systems officer and Intelligence officer. The first being the more active role, the latter being the safe option as I already have relevant civilian experience. However, the careers advisor has informed me that having two roles in mind whilst doing the selection is fine, if you're not suitable for one you may get offered the other.