We too have been backpackers:
http://www.dwilliamson.com/rvhist/Page.html
and have had three fifth wheel RVs: our first a used Prowler Regal with front living room, our second a new Jayco Eagle, and our present Montana 2955RL (2002 model year). The Designer is a nice trailer and we were considering it when we found our Montana (on a trip to Florida--we bought in Panama City from RV Connections).
We prefer the 2955 to larger Montana
for our own use. We are not and never will be full timers. I prefer to tow and park the smaller trailer.
In short, I don't think you would go wrong with either the Montana or the Jayco Designer. I have not made a careful comparison, but that is my impression. Spend some time in the exact models of each which you are considering before making the choice. The one that "feels right" is the one you should get.
Email also sent via Forum