Dolly; one time investment, universal-can tow most vehicles, no need to buy new stuff if you want to tow a different vehicle. Its a little more time consuming to hookup and disconnect. Very nice if you are a franchise of the "Dads, Auto repair and Towing service".
Can be backed a couple feet (i.e. overshot the gas pump and need to back up 2-3 feet), Anything farther than that will require a great deal of practice.
4 down; purchase/investment cost generally dedicated to one TOAD vehicle. However, some of the investment can be re-used if you buy another TOAD, (maybe)
Tow bar - might be able to use on multiple TOADS, If the TOAD is equipped with the same manufactures base plates that match the tow bar.
Base Plate - These bolt to the frame of the car and are very specific to the car. The Tow bar then attaches to these plates. Base plates are a one time install on the car and cannot be transferred between cars (unless its the same make/model,year, etc)
Brake system - Some can be moved from vehicle to vehicle, but may require small modifications to the vehicle to accept and use the system. Some are are dedicated and cannot be moved.
4 down towing is a lot simpler to hookup/disconnect.
Also - Backing with a TOAD is entirely possible - check with your tow bar manufacture to make sure its OK with them, and also you need to verify how the TOAD steering behaves while backing (castor). If you can back a trailer, you can back a TOAD. I have no limits on mine, I've backed it into parking spaces at campgrounds, truck stops, etc. like I say, mine is just like backing a trailer.
2001 Coachmen Mirada (Ford F53 6.8L V10) - Toad 2001 Civic
It won't do MACH 2, but I can get a sandwich and take a pee.