I'll have to run with another thought here... I personally don't think the minor differences in the trailers between most of the manufacturers is a big enough issue to completely direct my direction in purchases. I'll grant that some are 'better' in certain ways, but there is no way I could definitively decide that one had a greater value longevity wise over another. With that...please keep in mind, I'm not buying the cheapest of the models. There is a point where the flooring stringers are so far apart, thinner plywood, etc, where they just can't hold up to anything beyond a mattress. A $3k trailer is just that...it will pull and keep stuff covered, but I wouldn't be putting a bunch of heavy point load items in there.
Currently, we have new Cargomate and Continental Cargo trailers, a Haulmark, a Wells, a Pace, a Mirage and some commercial cubes. I've owned several others, including Interstate. Add our flatbed equipment trailers and other various types of trailers, and wheels, axles, frames, etc, are obviously well known to me. My point is, I get to compare them all, hence my less than pointed opinion about where to look.
I don't like 14" tires, so they're not an option. We're almost entirely 16", but that is not a viable option on a light duty trailer (brutal ride and overkill) so we do have some that have 15". Almost all the axles are minimum 5k, and although I love torsion for lot's of things, they suck for replacement. Not the work, that's easy. But around here, they are almost 100% custom, so your trailer is down for the 6 - 10 weeks while waiting for a replacement. Ask me if if enters into our decision on which to buy? Pretty much never.
Doors are doors, the skins are all super light and flimsy. But they keep the elements off the stuff. We have both ramp and cargo units; they all serve a purpose.
I've never seen anyone complain about having an extra few feet, so with that, if you think you need 16', get the 20. The difference in towing is not even worth thinking about. When you get up into 28, 30 and 32'....it can something you have to deal with and plan for (gas stations, etc).
We extend most or our hitches.. they tow better, jack better and lessen the chance of connecting (turning 90 degrees on flat isn't the problem...do that with the truck on an incline and you'll find out that the camper is a whole lot closer than you thought).