So WE have Liquid,Solid,Nuclear Thermal,Batteries and Monopropellant Fuels but Liquid Fuels should be a selection like solid fuels and under the liquid fuels when selected should have selections of Fuels (Kerosene,Alcohol,Hydrazine,Methane and Hydrogen) which have different Efficiencies and Oxidizer (Liquid Oxygen and Nitric Acid) which also has different efficiencies with the fuel.
Solid Fuel when selected should also have a configuration selections like these:
and they should have different burn times,thrust and efficiencies
@Kell then let's decrease efficiency.If you just don't want this suggestion i'll just delete this.