In the near future most machinery will be used for construction of buildings and infrastructure and most people will use flying cars (maybe). Most of these services will require more torque, which means more power, which means more diesel engines! Even though you get more torque with diesel, you lose speed, so flying cars won't be racing cars. If you wanted a fast car, you would use gasoline, which has more horsepower at higher rpm. Although most machinery will use diesel, for some people public transport will be mainly petrol-powered, while most people will use the diesel vehicle for towing things or for construction use. When you require power you will choose a diesel, but if you require a "fast" utility (e.g. sports cars) you will choose petrol. With this in mind, the final question is which fuel is more earth friendly because we all know that Mother Nature should be taken care of