I tow with a dolly because I did not want to invest in new/different cars to tow. I currently tow a Mazda 3 with a dolly. No difference in milage with my DP. Only issue is with smaller cars like mine, you have to have a small ramp (I use two 2X8) just to raise the front a bit or the plastic under the front bumper will rub on the tow dolly ramps. I would eventually like to tow 4 down but it is a lot cheaper (at least initial cost with the car that I already had) to go with a tow dolly.
I don't ever try to back up.