Standard. I talked to Ben at Dynamic, we were thinking of getting a set of the big wheels, and he said that only in the most extreme cases does he feel that the larger wheels are needed. He suggested lowering air pressure in the tire down to 10 psi as an alternative.
We don't go through deep and very soft sand, and have not had issues with our dollies with standard tires in medium sand.
You can call Ben or Chris at Dynamic and get good info from them. If you decide to go ahead with the purchase, send us a PM, we are e-Dealers and can get you free shipping in CONUS.