I have done both, and I have put a vehicle on a flatbed trailer.
My truck is set up to tow four down. My PT Cruiser can be dolly towed, or I could install a lube pump and the baseplate for four down towing
There are pros and cons to each method. A search on this forum will likely turn up many discussions.
Most front wheel drive cars can be towed on a dolly.
Many vehicles can not be towed four down without expensive (yes, IMO, $700 to $1000 is expensive) modifications (lube pump, etc.). Then add in the cost of the towbar, braking system, lighting, etc.
A good dolly can be delivered to your door for about $1500 (http://www.americancardolly.com/). Or, you can buy a Demco for about $1700 (T1210) to $4000 (Kar Kaddy II) new or $2000 (more or less) used.
4X4 and AWD vehicles can not be towed on a dolly.
Most 4X4,s and some AWD vehicles can be towed four down.
Many rear wheel drive vehicles can not be dolly towed or towed four down. However, by disconnecting the driveshaft, they can be towed either way.
Whether you are dolly towing, towing four down, or on a trailer, you should stop after no more than 50 miles and inspect the tow to ensure that nothing has gone wrong. It is simply a good safety practice.
The best source of towing information about a vehicle is the Owner's Manual.
One can also check the REMCO website for information.
Motorhome Magazine has a pretty good list of towables.
It all boils down to personal choice. What do YOU want to tow, and what are you willing to do or willing to spend to accomplish it?