Trip to Australia in December (Sydney)

Hello! My husband and I are planning to come to Australia during the Christmas/New Year's Eve holidays.
Does anybody have tips on where to go, what to do and so on?
What cities are worth to see?
Should we rent a car and drive along the east coast? west coast? We love hiking, surfing, and any sport available!
We are looking into super expensive places, but at the same time we are not hostels people ;)

Thanks :)