I'm told that a Dolly is a little easier on the toad than four-down. Naturally, Dolly precludes some of the odd behaviors that late model cars with ABS, Stability Control, Electric Steering and all that have brought to the table. I'd still go four down.
For me, the biggest advantage of a Dolly is versatility. If you have several vehicles, share vehicles, or change vehicles often, then Dolly makes lots of sense. Dolly is cheaper than having an RV dealer, CW (which I don't recommend) or other shop furnish and install all the four-down stuff. Our coach came with a dolly that I probably sold too cheap but was already tired of jockeying it around. I avoided most of the four down cost by installing my own base plates. Done four on owned vehicles and helped with a few others. Last base plate and tow bar I bought were both used.
Dolly with Surge Hydraulic Brakes is a little more versatile than one with Electric that requires a Controller and on-board Battery. That's because you can tow it with a vehicle without a Controller. So that'd be the deciding point for me. If I was pretty sure I'd use it only with our RV, Controller and Electric Brakes, especially if the Dolly was going to sit idle months at a time between uses. Hydraulic brakes spoil with standing. Stuff sticks. IF Hydraulic, I'd want Disc not Drum, brakes.