We looked at most of the dollies a few years back and finally ordered the King of the hill a DEMCO Kar Kaddy SS. The best price I could find was through PLP Motorhomes in Texas. At the time we lived in Fresno, CA so they shipped it via truck to our then home.
I was surprised as anybody when the huge crate came un-assembled. Once unloaded the crate barely fit into my garage. We put the whole thing together. The instructions were great. We had a few calls to DEMCO customer service, but we got it assembled and have had many tow's with it and no problems at all.
Yes it is the best and most expensive, but in my book you get what you pay for. We are towing a Lexus SUV and it goes right on down the road.