It depends on what you want to do with the air compressor. If it's for air brakes, then you'd have to run it off the engine. If it's just to fill a tank for an air horn or an occassional tire fill, then electric would be the best to and easiest. If you want a serious air compressor for painting, sandblasting, etc, then mount it in the bed and drive it with v-belts off the pto. Heck then you could put all your horsepower into a big compressor. .