The 3 most important things to me are:
1. Steerable wheels. With steerable wheels the dolly follows directly in the path of the rear wheels on the motorhome. It doesn't cut the corners like stationary wheels do, so you don't have to make extra wide turns to avoid running over the curb or other objects.
2. Electric brakes. The brakes can be set for the load you are carrying. Depending on the controller you use you can set the initial braking pressure, time when the brakes activate in relation to those on the motorhome, and keep them applied on an incline or decline. You can also manually activate them if necessary.
Check your manufacturers recommendations. Some manufacturers advise against the use of surge style brakes on a dolly or trailer especially if you use a drop hitch.
3. Self storing ramps. With self storing ramps there is no need to get under the vehicle to install or remove the ramps when unloading and loading. There is also no need to store them when traveling. They make the loading and unloading process much simpler and cleaner.
When we tow our Buick we use Roadmaster 2000-1 dolly. Along with the other features it has lockable storage compatrments for the wheel straps and other accessories when not in use. It has built in tie down ratchets, safety chains, and lights. It's not the cheapest dolly in the world, but it's well built. We've had ours over 12 years and used it over 25,000 miles without a problem.
We don't use it as much now as we did years ago primarily because we've gotten into off roading. It's sorta piontless to haul the Buick half way across the country and leave it at the campground when we rent a Jeep. Most of the time we take our Jeep Wrangler along, but when we go places that don't offer off roading we put the Buick on the dolly.
