In Sydney we stayed at the Sheraton on the Park. It's a beautiful hotel in a great location. There's a subway station right across the street so you can ride from the airport to the hotel very easily with getting a rental car which I think would be a hassle in the city. If you opt for this hotel, get the club floor passes. Their breakfast, dinner, and booze really helped keep cost down
Public transportation in Sydney is great. Really no need for a car.
Other items we really enjoyed in Sydney:
- Like mentioned above, the Toronga Zoo is not your typical zoo. It offers incredible (the best?) views of the Sydney and the opera house along with incredible wildlife exhibits and shows. Be prepared to walk, hike, climb.
- The Rocks - get a reservation for a restaurant and have dinner there. It's a local hangout area and is beautiful at night with all the old streets and buildings.
- Ferry to Bondi or Manly beach. Pretty typical beach type areas but a nice day of relaxation and drinks
- Koala Park Sanctuary: my wife wanted to interact with koalas and kangaroos so we took a long subway ride and a taxi to this place. We had a small group, interactive opportunity to feed, pet, and take pictures with koalas, kangaroos, and other wildlife. Like an Australian animal petting zoo of sorts. Very cool.
If you head plan to head to Perth I could start another list but that's a loooooong ways away
Have Fun!