Which one is better to buy a petrol car or a diesel car?

There is no better. Each has plus and minus. Diesel has more torque (pulling power), will last longer, gets better mileage, but cost more to buy and maintain. Diesel fuel is also more costly. Petrol is cheaper to build, costs less to maintain, normally has more horsepower, and gasoline is cheaper than diesel. The decision on which to buy is much easier to make today due to how clean diesel engines are now.
patrol cars are better than diesel ones if the use is very less.