I have ttowed both ways. I find the 4 down option a little better than the Acme dolly that I had. I just bought a 2011 HHR that I set up to flat tow. I flat towed a 2008 HHR for about 80,000 miles. The problem going forward is in choices of tow vehicles that can be flat towed. Many of the new cars cannot be flat towed.
I found it fairly easy to dolly my 2015 Chrysler 200 and not too much longer to get it ready to tow.\
You will find the cost to dolly tow is less investment and you will have a choice of toads. Flat towing means you will have to dedicate a vehicle to tow.
As far as costs a Dolly can be purchased used between $750.00 - &1000. for a good one with surge brakes. Add the tie down straps to the cost and you get a total investment ( in my case ) of around $900.00 on the other hand to set up and tow my HHR I had the cost of Base plate, Tow bar, Light wiring and diodes, Ready brake,and misc connection cables. Total cost to set it up right at about $2000.00 I did the work myself so add another $1000.00 to get all of it installed.
The up side of 4 down is a little easier to get ready to tow and the lack of need to store a dolly.
The down side of 4 down is that you have a dedicated toad and if anything happens to it you cannot easily switch toads without repeating the set up expense.
Again with the Dolly you can tow a number of different toads without additional expense so switching cars is easier and a larger selection going forward.
I am retired so my HHR does not get many miles and should last a long time so it is 4 down for me.
BTW. if your toad requires a fuse to be pulled it is easy to make or buy a bypasss switch.