Well, luckily for you, I work in car insurance, and my wife works with CTP!
Firstly, the difference between insurances:
CTP (Compulsory Third Party, or also known as a Green Slip in some states): This is part of your rego and it covers third parties who might be injured in an accident where you're at fault. This includes people in your own car. Some insurers also extend this cover to the driver at fault, so even if you cause an accident, you can claim for your own injuries as well. My personal suggestion is that you go with one of those insurers. Its compulsory, as the name suggests.
TPO (Third Party Only cover): This covers you for any damage you might do to other parties' property where you're at fault in an accident. Everyone talks about hitting that Mercedes or Rolls Royce, but you also need to think about things like fences if you crash into a yard, or armco or light poles that you might hit ... the govt DOES charge for these things, and they ain't cheap! The cover is very cheap and could literally save you thousands. Most insurers also include some cover for your car if you are hit by another driver who doesn't have any insurance, up to $5,000 in some cases. My personal suggestion is that if you're driving a car, and you don't have at least this much cover, then you are truly an idiot.
TPO + Fire and Theft: This is the same as TPO, but your car is also covered in the event of a fire or if it is stolen. Check with your insurer as to the full extent of this cover, as "theft" might only refer to the car actually being taken away, it may not cover attempted theft. Not all insurers necessarily offer this sort of cover, though.
Comprehensive: Covers you for all damage, to your car and other property. Its the most expensive, but it does pretty much cover every possible scenario, unless you're silly enough to do something illegal. Some insurers can also give you a reduced price if you don't drive the car often, or even if you don't drive it at all.
A bit long winded, but hopefully that explains it for you.
sigh~
