Depends.
Most gas pressure washers do not have water pumps. If you plan on using a tank, you would have to find a pressure washer with a hose inlet that is lower than the outlet for your tank, well, because gravity. And even then, you would have to worry about inclines an etcetera. Most electric power washers have pumps built in, so really no need to worry about gravity.
I've used gas for a while on a mobile truck, with a 110 gallon water tank. However, it died today and I'll be taking an electric pressure washer with me tomorrow.
So answer, gas with a water pump so you can get optimal use, or electric without. It depends on your setup and how you plan on using it. If you have any questions you can PM me.
Sent from my iPhone using Tapatalk