The diesel versus petrol argument could long be debated however, the total distances travelled each year and what the vehicle is to be used for are still the best guidelines to use.
Diesel will always come out on top when comparing straight out fuel consumption (like-for-like engine/vehicle size) but annual registration costs are around $130 more.
Add to that, the latest petrol engine technology is producing very low claimed fuel consumption figures, which in turn reduces emissions.
Fuel consumption is better on diesel, but the higher combustion temperatures required to burn the fuel can lead to increased levels of nitrogen-oxide (NOx) emissions in comparison to a petrol engine.
The general rule of thumb is diesel starts to come into its own more if you are travelling in excess of 20,000km a year or the vehicle is used for a heavy work load or towing on a regular basis.
The budget:
$40,000
The shortlist
Toyota Prius c
Something of a curve ball for you, but at last there is a hybrid (petrol/electric) vehicle on the market that looks funky, is practical and competitively priced (base model is $30,990 and the high spec'd s-Tech is $35,000). Claimed fuel consumption of just 3.9l/100km (using the cheaper 91 octane) looks pretty good when you consider the on-going uncertainty over fuel prices.
VW Polo GTi
The engine is somewhat complicated with a twincharged (turbo and supercharger fitted) induction system along with a 7-speed Direct Shift Transmission (DSG), but you can't help but admire the performance (132kW) and claimed combined fuel consumption of just 5.9l/100km. It's a potentially high-risk vehicle to buy in the used market (as the mileage and age increases) because of its technical complexity, but a new ($38k) or low-mileage ex-demo model would certainly put fun and excitement into your drive. There is also the less complicated Polo TSI (turbo only fitted) and cheaper ($31,500) to consider.
Suzuki Swift Sport
The Sport model has the performance to match the looks and represents great value for money ($27,500 manual and $28,990 auto). The Sport is well equipped in terms of body kit, driver comforts and safety. The uncomplicated and naturally aspirated 1.6 litre engine produces an impressive 100kW of power and returns a combined claimed fuel consumption of 6.1 l/100km (CVT auto) and 6.5l/100km for the manual.