I was going to go the 4 down route until I saw a friends tow dolly. The Acme dolly with the surge brakes he has is pretty slick ($1,200). A good dolly does have some advantages as there are a lot more choices for a towed vehicle, you can easily switch vehicles, they are cheaper. No extra wiring, pumps, lighting hook up, etc. needed. Lock the steering wheel and it's easier to back up. Backing up 4 down is pretty much impossible.
The draw back is it takes a few more minutes to load and as stated above you can't tow most 4WDs. Something I can live with.