I am in Qld so can't help you for SA but whoever you do end up with ask other agency staff members what they think of the company you end up choosing. I have worked agency for 16 months and in that time I've seen quite a lot of nurses change agencies due to better pay conditions, getting paid on time, uniforms provided and how easy it is to have contact with the staff of the company. Also, not sure if you have done agency before but different hospitals etc pay different rates and expect more work - point being I can do a night shift and the pay can be as big as $30-60 difference and the workload 29-46 pts shared amongst 2 staff members. It's like anything but I do refuse to work for certain hospitals.
Sorry couldn't be of much help but if you haven't done agency these sort of questions are important.
Good luck with it.