Dolly towing gives you the flexibility to tow more cars than flat towing. Dolly towing is basically a one time investment unless you wear out the dolly. Just keep in mind not all cars can be dolly towed but it's a small list. Dolly towing means you have one more piece of equipment to deal with and takes a bit more time to hookup and unhook/store when done.
Flat towing is easier to deal with on a day to day basis ( my opinion ), takes me less than 5 minutes to hookup when heading out. It does take a small investment each time you swap tow cars and the number of cars that can be towed flat is diminishing but currently there is a large assortment.
I choose my Chevy Sonic ( automatic ) back in 2014 as it can be flat towed, wife can drive it, and its fine as my daily driver. My next car whenever that might be will also have to be flat towable.