I would recommend pneumatic tires as it will allow you to roll over cracks or bumps much easier. Mine are about 10" in diameter For example the ramp up into the trailer, a solid wheel would have been really difficult to use. The guy that did my convertible top had a gravel drive, which also would have been impossible to move solid wheels on.
I used the casters like in the pic, the casters with the phenolic tires and they are actually pretty good. I've moved mine around on concrete, gravel, trailers, etc. There's not much weight once the front clip is off. I can lift the front of the car up in the air by hand.
