IMO, the DEMCO Kar Kaddy SS is without a doubt the best of the best when it comes to car dollys. Yes, they are expensive. I recently saw a used one, with surge brakes, that they were asking $1900 for. A new one is about $4000.
The American dolly is a nice one. It has electric brakes and turn table steering, and is about $1500 delivered to your door. BUT, it has removable ramps.
I would not consider any dolly that does not have some means of steering, whether king pin (DEMCO) or turn table (American, Master Tow, and others). No matter what hype their advertising puts out, an unsteerable dolly will never be in my yard!