Having owned both petrol and diesel vehicles, in my humble opinion, there are two main advantages for 4WD diesels.
1/ range in the outback, which includes torque, etc, etc.
2/ availability of fuel in the outback
Petrol vs diesel models - purchase price, resale, service costs, economy all seem to reach a common denominator after some time.
In other words, if I bought a car or 4WD for the city and local environs, I could probably buy a petrol.