The best engine for you depends almost entirely on how you actually drive — not on what is fashionable. Be honest about your weekly pattern and the answer usually picks itself.
Petrol
Cheapest to buy, simplest to maintain, and serviceable almost anywhere in the country. Modern small turbo-petrol engines are efficient enough for most people. Best suited to short trips, suburban driving and buyers who want the lowest purchase price.
Diesel
Strong pulling power at low revs and excellent economy at highway speed, which makes it the natural choice for towing a caravan or boat and for people who cover big distances. The catch is that diesels dislike a diet of short trips — the particulate filter needs regular longer runs to clean itself, and repeated short journeys can clog it and lead to expensive repairs.
Hybrid
A petrol engine paired with a small electric motor and battery. You never plug it in. Hybrids shine in exactly the conditions that hurt normal cars — stop-start traffic, school runs, city driving — where they can use dramatically less fuel. On long highway trips the advantage narrows. A very safe choice for most Australian suburban drivers.
Plug-in hybrid (PHEV)
A bigger battery you charge at home, giving a useful electric-only range for daily commuting, with a petrol engine for long trips. It suits someone with a short commute and off-street charging who still wants to drive interstate without planning. If you never plug it in, you are just carrying heavy batteries around.
Electric
Lowest running costs by a wide margin if you can charge at home, especially with solar. No fuel, no oil changes, far fewer moving parts. The trade-offs are a higher purchase price, the need to think about charging on long trips, and the importance of having somewhere reliable to plug in. If you rent without off-street parking, this is the question to answer before anything else.
How to choose
Work out your weekly kilometres, how many are city versus highway, whether you tow, and where the car sleeps at night. Those four answers narrow it down faster than any brochure.