Personally I carry two types, there are many types of fire so you have to assess your situation first, for many a high risk are gas fires from cookers and fuel fires from refilling fuel tanks from containers and both require a different approach.
I used carry a CO2 as these instantly knock out the air and flames to stop s fire spreading, but have no cooling capability and as such anything heated such as metal can re-ignite leaking gas or other fuels which means you have to get both CO2 and instantly hit it with water to cool any hot metals to prevent re-ignition.
Dry powder is a good alternative to CO2 but as usual they have downsides, with an underbonnet fire CO2 will kill it dead and being CO2 it will also stop the engine as the air filter digests the CO2, but dry powder smothers to expel the air and it creates an awful mess, and it cannot be used to stop an engine as it does more damage than a little.
My other preferred alternative I carry is a foam extinguisher as this is great for spilt fuel fires but you have to know how to use them, you begin by spraying off the fire and roll the foam over it, this smothers it and as the foam breaks down it cools it so you have something fine for conductive surfaces such as metal as you smother and cool at the same time.
One thing I regularly carry is a 10 litre pump up garden sprayer such as a Killaspray or Hozelock as these carry 10 litres of water and have an adjustable spray head which with a simple twist change the spray from a fine mist through to a jet spray, these are invaluable when used with CO2 as you hit it with CO2 to knock back the flames and the water at the same time to provide cooling to prevent re-ignition. They also have other uses, if you are off roading and the windscreen is filthy you use it as a jet to spray the windscreen first without using your wipers and damaging your wiper blades, you can use a jet to spray your radiator from inside the engine compartment to unblock it when it is blocked with mud, or just blast mirrors, door handles, lights, and even your fuel filler cap to remove mud, you can even use them to clear brakes if you have an ABS equipped vehicle.