Attend every opportunity you get invited to, as you shouldn't count your chickens before they hatch. Also the more interview experience you get the better your chances. They all tend to use the same format so if you get stuck on the questions with the first airline, the second airline will probably use similiar questions. Also cabin crew recruitment process takes a long time from the asessment day to the job offer so give them all a go.
Also I've heard Qantaslink pays you during groundschool where as Rex doesn't. And that Rex doesn't offer a job untill after you have completed groundschool and a position becomes vacant where as with Qantaslink your guaranteed a fulltime position when the offer is made for groundschool.