Hi Smithy
A lot depends on your individual circumstances but if you plan to turn the PPoR into an IP, an IO loan is usually the best way to go. This will maximise you tax deductions when the property converts to an IP. For example, with P&I if you owe $180k when you convert to an IP, only $180k of interest will be tax deductible. With IO, if you owe $230k and have $50k in an offset account (which you use for your next purchase), then the full $230k will be tax deductible.
One circumstance where it may be better to pay P&I, is if you aren't very good at saving / budgeting. By paying P&I, you can use it as forced saving.
Keep up your learning by reading the forum and feel free to ask questions. Note I am not an accountant and you may need specific advice.
All the best