IMO, the Kar Kaddy by DEMCO is quite likely the best car dolly available. However, it is also very possibly the most expensive! There used to be two different sizes made. If that is still the case, be sure you get one that fits the vehicle(s) you will be towing.
As previously stated, almost any front wheel drive vehicle can be dolly towed. Almost! I have heard of some newer vehicles that can't be towed on a dolly, because when the rear wheels are turning but the front wheels are not, the computer gets confused.
4X4 and All Wheel Drive vehicles usually can not be towed on a dolly.
Rear wheel drive vehicles should not be towed on a dolly; transmission damage may result. A drive shaft disconnect may be installed, or the driveshaft can be disconnected and secured to the underbody. (this will also work with 4X4 or AWD vehicles). Some people have loaded a rear wheel drive vehicle on a dolly backwards. It is not recommended by dolly manufacturers, but when properly done it seems to work.
We towed our PT Cruiser on a Kar Kaddy dolly from Montana to Georgia and back. It really wasn't all that great of a problem. We had pull-through sites in all except one campground. That back-in site was the only time I had to drop the dolly.
We tow our Jeep 4 down with a fixed arm adjustable width towbar. Many people will say that such a towbar is junk and should never be used. I hook it up by my self quite frequently, and that old (20+years) bar has worked flawlessly.
If time is critically important, 4 down is a quicker hookup than connecting and loading a dolly. For me, time has never been that critical! 5 minutes to hook up the Jeep or 15 minutes to hook up the dolly and load the PT? The difference is really meaningless.
The only thing that is truly important is to choose wisely for YOUR needs!
Good luck.
CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"