4 down is the best way to go for most. But, that assumes you are towing the same vehicle all the time and that you don't change vehicles often. It can cost up to $3000 to configure a vehicle for towing 4 down so you don't want to be doing that often. If you want more flexibility, a tow dolly will be a good solution but it definitely comes with a lot of tradeoffs. Dead last in my opinion, and only for cars that cannot be towed with a dolly, is a 4 UP trailer. Good luck finding a place to put that thing in many of our Nation's campgrounds. To recap, I think it is a simple choice. If you have a car you're keeping for more than a few years, configure it for and tow it four down. Otherwise, suck up the pain of a tow dolly and enjoy the flexibility. Your cost will be about the same either way.
Randy and Tina & pups; Cinnamon, Cookie & Coco
2010 Winnebago Journey 34Y
Freightliner / Cummins 340hp ISB, 2014 Ford Focus