trailer quality

As a very general statement from best on down
Airstream, fiberglass eggs, Oliver, Northwoods rv, outdoors rv, Lance, now you get into the true mass marketed units, others may (and no doubt will) differ, but here is my opinion based on what I've seen.
Grand Design, K-Z, Jayco, Winnebago, and then the thundering herd.
Some upper end models from Keystone or Forest River may have more fans than others, but as a generalization, this will give you a start.
As a starting point consider warranties, their value is questionable because of dealer support, but some lines offer longer warranties which COULD be seen as a sign of manufacturer support.

I’m happy with my WInnebago and the whole towable Micro Minnie line is within your length limits.

Oliver and Lance come to mind.
You could also check out Airstream if you can live without a slide....we can't.