I just did a bunch of research for a trailer purchase of my own. I think united ,stealth, storm, look, haulmark,wells cargo, atlas and carry-on are all pretty solid steel trailers. Make sure to look at storm brand, they are pretty damn nice and less cost than stealth or united. Look and Haulmark are going to be the cheapest of that group.
I would stay away from the bargain southern trailers like gatormade, x-tra tuff etc.
I would recommend getting 16"o.c. floor and ceiling support spacing, 6'6" interior height & ez-lube hubs, LED lights, water resistant 3/4" subfloor. Spring axles are fine, radial tires are a nice upgrade.
Don't buy one with a 48" tongue get a 60" tongue, it makes a big difference in the maneuverability when backing up.
You can tell allot about a trailer if you remove a piece of interior trim to see whats going on, also pull one of the clearance lights, if they use a grommet to protect the wires or did they do it down and dirty and just drill a hole and stuff the wire through.
Haulmark has been around a long time I have owned several of them from 14' to 44' . Never had a single issue with them. I have a storm 14' Motorcycle trailer now that has been a very good trailer. i'd say stay with a known brand that has been around awhile.