Originally Posted by Racemosa
Besides Airstream ( no slides)
You do not define 'best'. Is it lightest, the one with the least wind resistance, least sway, longest life expectancy, etc? Airstream would be my first choice and if you are looking for a slide out model, go to the Airstream forums and there is lots of info there on the slide out models. As far as longevity the AS will outlast any four or five box trailers.
Northwood AF trailers are heavy but are marketed as 'four seasons' if that is a consideration that matters to you. You have sufficient truck to pull one as they are heavy, some models over 10,000 pounds. They come from the factory with their own frame, shocks on the axles, and the higher end models are aluminum construction in the walls.
A good used Avion will provide years of service, some models are triple axles as long as 34 feet, and will cost a fraction of a new trailer from another manufacturer. Their construction is solid and during the years they were built actually were considered by many to be better built than Airstreams of the same era.
In my opinion a good used Avion or Airstream is probably better than most new box trailers as far as quailty and longevity.
Good luck in your search.