Car Rental is always a good option for those looking at getting around the city. We recommend DriveMyCarRentals they have a range of ongoing deals and offers for cars in the Sydney area.
Keep in mind that you should have an international licence if driving in Sydney. The streets can get tricky especially if getting around the city. Parking for cars can also get tricky and expensive, so if you are renting a car plan ahead. There are plenty of parking garages and the best deals are for the Early bird rates which have entry and exit times to each garage.