Have you considered where you are going to store a trailer, both at home and on sometimes small campsites? And yes, there is the weight, and gas mileage, issue. Or are you perhaps talking about a tow dolly, which is a different beast? I can't say that I recall ever seeing anyone hauling their toad on a trailer.
In any event, my preference would be to use a tow bar because there is far less hassle, time and energy involved. The downside of doing so is that not all vehicles can be towed with all four wheels on the ground, so you have rather limited choices at trade-in time. Also, each such towed vehicle has to be equipped with brackets to which to attach the tow bar. Those brackets are not one size fits all.
As to backing up (with the toad attached) when using either a dolly or a tow bar, I believe you might find that to be just a little bit of a problem.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.