Amost all oil fired pressure washers are set up using diesel fuel. The red dyed stuff as there is no need to pay road tax for the udyed.
Kerosene will burn hotter but has less lubricity than diesel and may contribute to premature fuel pump failures. In most cases kerosene is more expensive than diesel any way.
You can also burn Jet A or at the other end stove/ bunker oil.
Each has a price quite different than the other and physical properties that are potentially not suitable for your application.
Burners are set at the factory using diesel therefore the airband and shutter settings are optimized for that fuel. The burners are manufactured to perform on diesel fuel too. Fuel nozzle size and pressure are determined using this fuel as well.
Changing to another fuel may change the light, burn, shut down and relight character of the burner. You may need to adjust the settings on the burner air band and shutter, fuel pressure and nozzle size to prevent sooting of the coil, incomplete combustion, excessive emissions, poor heating performance or excessive fuel consumption.
If you can get one of these other fuels at a truly competitive cost then it may serve you to learn how to make the required adjustments or pay someone to make them for you.
Remember that your altitude may also affect the burn character of your unit so look for the following: clean light (no smoke), clean burn (no smoke- test with a smoke tester to ensure a smoke of 3 or less; less is best), clean shut down (no smoke) and clean relight (no smoke).
Lots of possible work for doubtful benefit so stick with red dyed diesel and NEVER, NEVER use it in any over the road equipment because the fine can be really large.
Hope this helps? Cheers.