First off, why do you want to change your structure?
If you are self employed or at risk from being sued, you may want to look at holding them in a Trust to add a layer of asset protection. If your properties are negatively geared you'll rack up your tax losses to use when you are CF +ve or will need to have some form of income coming into the entity to offset the losses.
We are self employed via a company/trust arrangement. Most of our customers are US based, so I guess our risk of being sued is quite high (typical Yanks). We also have an investment company/trust arrangement. Our assets are purchased into our investment trust, and we move income from the business trust into the investment trust so we don't need to carry forward losses.
Other things to consider are land tax thresholds, accounting fees, annual company fees, bank account fees etc.
Cheers
Buddybee