Which Fuel is best for your car & for Environment .. BS IV or BS VI ??

This video is about condition of Air pollution in our country. Global ranking of India in terms of air pollution.what measure steps has been taken by the government to reduce the vehicle air pollution. All about BS IV & BS VI Fuel.. what are the key advantage of using BS VI compatible fuel .. even in BS IV vehicles. what kind of fuel is best for Environment ? and discuss about key differences between BS IV & BS VI Fuel. discuss about use of BS6 fuel in BS4 vehicles.