Historically, gas heating was the standard for Australian winters. However, with massive advancements in technology, modern reverse cycle electric air conditioning is now significantly cheaper to run and much more energy-efficient than gas heating.
Reverse cycle systems extract ambient heat from the outside air (even on freezing Blue Mountains mornings) and pump it inside, meaning they produce more heat energy than the electrical energy they consume. When paired with a home solar system, running a reverse cycle air conditioner during the day can cost almost nothing. Plus, you get the added benefit of cooling during the summer months from the exact same unit.