Not sure what you mean by Frog but here is my opinion...
Towing with all four wheels on the ground is easier as you have less equipment to deal with. But you have to equip each car you want to be towed and this is not cheap, and limits your selection of cars.
Towing using a dolly allows you to pick and choose what type of car you tow, and can swap them with out much hassle. You do have to deal with the dolly when you get to your camp site which for some people is a pain.
Towing with a trailer has the same benefits and issues as towing with a dolly but allows backing up. Some say they backup a car on a dolly, but I think it's not such a good idea.