I think that it's difficult to find a truly high quality manufacturer in the RV industry. Build quality, materials, and engineering are not what we would like to see, even at the purported high end. I believe this is true of both MHs and TTs.
Matters are complicated further by the fact that some of the largest manufacturers produce a dozen or more brands from the same production line and it's unclear how much the standards change. Quality isn't something you can turn on and off and if you have people with the background, training, and attitude to produce quality it's not as though you can cut their wages for four weeks while they make the cheezy trailers.
As you compare TTs, I would suggest that you mainly consider:
* Roof material.
* Exterior wall material.
* Frame material.
* Number, size, location, and operability of windows.
* Materials, workmanship, and extent of interior cabinetry. (You can spend $20,000 on kitchen cabinets for a stick house and a few TTs are built to similar standards)
* Materials and workmanship of furniture (do the mattresses have inner springs? Leather or vinyl? Nylon or polyester?
* Material choice for floors and interior walls. Fiberboard and OSB bad, plywood better, plywood with a larger number of thinner plies, best
* Presence of expensive components like larger fridges, second A/C, power jacks and levelers, electronics, awnings, larger brakes and axles than minimally necessary, detachable shore power cable, aluminum LPG tanks, spare tire, kitchen vent fan that actually vents, extra batteries, double pane windows, extra folding tables or chairs, fantastic fan, microwave
Consider that length by itself doesn't cost much. To add 4' of space with no appliances, cabinets, furniture is trivially inexpensive even with carpeting, slightly heavier axles, and a few more furnace BTUs.
The first thing I see when I look at a $17,000 trailer is not nearly enough windows. The second thing I see is kitchen cabinets made of MDF covered with a woodgrain decal. Mechanically (fridge, stove, freshwater system, wastewater system, running gear) there isn't any difference between that trailer and the $30,000 one, and realistically the design and build quality won't be much different. More windows, aluminum structural components in the walls and roof, and better exterior materials will be the main difference with maybe a little better cabinetry and more doodads.