Question

why gaseous fuels are better than solid or liquid fuel

Answer 1

Calorific value is defined as the amount of heat energy produced on complete combustion of 1 kilogram of a fuel. It is expressed in a unit called kilojoule per kg. The higher the calorific value of a fuel, the more is its efficiency.The calorific value of gaseous fuels are more.When a gaseous fuel  burns, it gives off a great deal of energy. And unlike other solid and liquid fuels it does not leaves any ash. 
and it produces very little air pollution.
Due to the above reasons gaseous fuel is always better than solid and liquid fuels

Answer 2

easy to carry
complete combustion is formed