Well, as one that started out dolly towing and very quickly realized it was not for me, let me see if I can break this down as to why 4 down is sooooo much better:
1. Ease of hook-up: With 4 down, you just pull the car up behind motorhome, slide out the tow bar legs, attach to base plate, hook up the wires and safety cables, and go. That is it. Takes two minutes.
With a dolly, you first have to hitch the dolly to back of motorhome (frequently requires wrestling the dolly in place, and some of them are not light). Then, pull out ramps on dolly. Drive car (carefully and cautiously!) up on the dolly. Then, secure the front tires to the dolly with straps (can be very muddy and messy, especially if its raining or muddy out). Secure the ramps. Hook up safety chains. By the time you do all that, it takes a LOT longer than it would to hook up when 4 down towing.
I've done both, I'm here to tell you, 4 down is MUUUUUUCH quicker and easier. Frequently much cleaner, too, in that you ain't crawling around in the mud and rain like you may be with a dolly.
2. On the road: With 4 down towing, you can pretty much take turns as tight as you want or need to in tight spaces (provided you set up the tow bar and towed vehicle right). You are not going to hurt anything.
With a dolly, you have to worry about tight turns causing the dolly fenders to make contact with side of the car. You have to worry about large bumps causing the ramps to hit bottom of the car. You have to worry about one of the tire straps wearing out, breaking, and causing a nightmare.
Overall, I found my level of stress on the road is significantly less with 4 down towing as it was when dolly towing.
3. At campground: With 4 down towing, you can unhitch where ever you want in 2 minutes, and go straight to your campsite. Tow bar folds up, don't have anything else to deal with, really.
With a dolly, you have to back the car off the dolly, then find somewhere to unhitch the dolly, and unless you have a pull-thru site, you have to wrestle that thing (dolly) to where ever you're going to put it. May have to even drop it off in a parking lot or storage space.
4. At home, when not camping: With 4 down towing, tow bar stays folded up on back of Motorhome. Nothing to do, really, except maybe occasional lubing, cleaning, etc.
With a dolly, you have to find somewhere at home to store that dolly. You have another set of tires to maintain, wheel bearings, etc. to take care of.
All that said....There is no denying that dolly towing is less expensive overall. Especially if you trade vehicles often and/or can't do any of the install work yourself. However, nearly anyone that has done both will quickly tell you that 4 down towing is muuuch easier and more fun, overall.
Will and Cheryl
2021 Newmar Baystar 3014 on F53 (7.3 V8) Chassis ("Brook")
2018 Jeep Wrangler JK ("Wilbur")