In 16 years of full-timing we've never gotten ourselves in a position to have to back up to get ourselves out of trouble so that's really a non-issue.
If you don't have a truck yet, one of a suitable size for a large 5th wheel is going to be expensive. Buy your 5th wheel first and then match your truck to it depending on the weights. If you already have a towable car, you have no added expense. Towing 4-down is the way to go. It's so easy.
We full-timed in both a 5th wheel and a Class A. We much preferred driving a car around siteseeing than the big truck. Our car also got better fuel mileage.
Motorhomes don't mind sitting at all so if you're planning to move every month or two or more, that shouldn't limit you.
We found that backing into campsites was easier with the motorhome. It's easy to disconnect the car, pull it into a nearby empty campsite or along the camp road and quickly back the motorhome into the spot. It's no big deal.
Can you tell....we liked the motorhome best.