My wife & daughter came with me on my business trips for a few months and we pulled her 2012 Focus with an articulated dolly most of the time. We eventually changed over to a tow bar because the dolly weighed 800 lbs by itself. I figured that the reduced weight would improve braking. It did, but the geometry hurt cornering.
We traveled from Charleston SC to St Louis, MO to Fresno CA, and to Seattle, WA. There, I installed the tow bar and we went back to St Louis and then back to Charleston. The dolly was very stable on flat roads, but the mountains were challenging. Climbing a steep grade in NC, the truck's rear end broke loose and we fishtailed pretty badly. Fortunately, I was able to recover with no damage. Coming downhills could be a little nerve racking having 4,000 lbs pushing on you with no brakes other than the truck's. We had a deer run out in front of us out west and I was surprised at how fast the truck slowed despite the weight. Another disadvantage to the dolly is that your car's front end is up, so the rear end is down plus you cannot back up an articulated dolly. We scraped the back bumper on a few driveways and we got trapped in a small parking lot where I had to unload the car, turn the rig around, and reload the car. You can back up a non-articulated dolly, but you are badly limited on turning radius as you have to drag the dolly sideways through turns.
A tow bar has much better braking as you can add a brake buddy. Even without one, it is a faster stop than a dolly. The car is also closer to the truck and lower to the ground giving much better gas mileage (16mpg with tow bar vice 13mpg with the dolly) and it is more stable and less likely to fishtail because you only have one pivot point instead of two. The bad thing about a towbar is that the centrifugal force of the front half of the car is transferred to the truck while cornering. It is like pulling a shopping cart around a corner. While using a dolly, the dolly's wheels take this force for the truck. As a result, using a towbar makes it very easy to fishtail the truck around corners, especially in the rain.
Most people who use a dolly on a one time trip use U-Haul. I have used these before and they are an articulating type like what I had. Thus the U-Haul dolly has all the disadvantages listed above. Their car trailers aren't much better. The have a surge brake on only the front axle which means not the best braking ability. Their trailers are also HEAVY, so the weight cancels out any braking effect you might get. Also because U-Haul feels you should never be without the brake, you cannot disable it. As a result, it is almost impossible to back up and if you hit your brakes fast and hard on slick pavement, the trailer will pass you. Ask me how I know.
If you are indeed planning on getting a U-Haul dolly (which I recommend over the trailer), make sure you get the extra insurance and you set your ball height high enough that the wheel pads are angled up about 15 degrees. This will help keep the car on the pads in an emergency stop and prevent the pads from hitting the underside of the car when going over driveways and speed bumps.
RK
