I have done all three methods (four down, tow dolly, and car hauler trailer).
four down is nice, IF your vehicle can be towed that way. Some vehicles can be, some can't without expensive modifications. I towed Jeeps, a Corvair, and a dodge 4X4 four down.
A dolly is great for front wheel drive vehicles that can not be towed four down. I towed a Chrysler PT Cruiser from Montana to Georgia and back. No problems.
A trailer is great for any vehicle up to the size/weight limits of the trailer. I have towed AMC Eagles on a trailer. I have also towed Jeeps on a trailer, when I didn't want the wear and tear of long distances on the tires and drive train.
As far as cost, it is pretty much a wash. A good used dolly can be purchased for 500 to 1000 dollars. A new one for 1500 to 4000, depending on brand.
A towbar and all the gimcracks and gadgets can be had for less that 500 dollars used, or several thousand new, installed.
A 16 foot trailer with 2 foot "beavertail" can be purchased for less than 2500 dollars new, ready to go. Four tie down straps or chains can be anywhere from 15 to 50 dollars. Used trailers can be anywhere from 500 to 2000 dollars.
Then there is backing up to consider. NO towbar or dolly manufacturer that I am aware of recommends backing. Some people say they do it all the time. I tried it once with a Jeep on a towbar; made it back about 5 feet when the front wheels SLAMMED violently over against the stops in a full left turn! I will never try it again!
A trailer can be backed anywhere, anytime, any distance, depending only on the skill level of the driver. A trailer can also be used for other things when needed. I used mine to haul hay for the horses. When I had horses.
Now, what is best for YOU? That is a question that only YOU can answer.
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!"