In the size range of the Mini / Fiesta mentioned above, I am towing a Chevy Sonic with 4 down. It is one of the few compact cars with automatic transmission that needs no significant alterations to tow.
The only requirement that GM has to tow this vehicle was the removal of a fuse to prevent battery drain. I eliminated that nessecity by adding a charging cable connected to the 7-pin plug with an inline fuse to protect the battery. It was installed by my dealer at the same time as the towing plate for no additional cost.
So far I have loved the car. it is my daily commuter as well as the Toad. Decent power for a compact, lots of space for four adults and the dog and tons of trunk room for picking up groceries or storing extra items while in transit.
If you want really small, the Chevy Spark also tows 4-down without any additional alterations.
Griswald One - Life is a Misadventure!
2015 Greyhawk 29ME / Chevy Sonic