As some have already stated, most manufacturers buy from the same suppliers. Custom built, stand alone companies, in my opinion may have better built frames, which like a house foundation, is the basis upon which sits your house. There are very few trailers made with a "boxed", or square tube frame, but these are a better choice than the standard I beam. It is also my opinion, in an effort of manufacturers to improve towing mileage, frames have been lightened, or spec'd to minimum requirements.
Do make sure you get a trailer that has very good insulation and double pane windows. Our previous unit did not have good insulation, or the windows, and we were cold when the temperature got down around the freezing mark. We'd go through a 30 lb. bottle of propane in a day and a half trying to stay comfortable!
Our present unit, a 2014 Open Range, with the dual pane windows, heat pump AC, and fireplace is very stingy on propane. We have been away from home since mid January and have not used 40 lbs. of propane yet! This is by far the best insulated trailer we have owned. Not sure I would full time in it though considering what I said in the first paragraph.
Good luck,
Bandaid