... What is important to some means nothing to others. ...what works best for one will never work for another.
I agree completely, however there must be some common ground with which they can be fairly judged. Basics for an offroad trailer.
Ground clearance would be one. This will likely be more due to tire sizes available. Breakover angle and the vulnerability of the under side would be deciding factors too. That said, a tall trailer should not win the category. Center of Gravity should be part of the equation.
Suspension does need to be a part of it. Shocks are needed. Tires and springs should fall into this too as it all needs to work well together. Leaf springs have indeed served many miles on military offroad trailers.
Body Tub or shell it needs to weather the climate and conditions. Shielding for the front where mud and rock are thrown. Steps and sliders. How easy is it to load and deploy. Is the interior sealed? How about clean-up after a trip? Lots to consider.
Hitch. Sure Pintles articulate, but they can also be harsh and noisy. A ball coupler offers less articulation, but is nice and quiet on the trail.
Electrical system, including lighting. Some will have the frills of a communication system and entertainment, but even just good running and stop lamps are a nice thing.
Kitchen. Rated from a shelf to put your stove on all the way to the built in garbage disposal model.
Bunk. Sleeping amenities. Flop a tent beside it, or crawl into a ready made bed. Plenty of range. How long does it take to be ready for some Zzzz?
Cooler Extra points for a fridge. A good ice chest is nothing to be ignored though. Both would be a bonus.
Water Tanks , jugs, bottles, drinking , washing, as well as the manner in which the water is dispersed. Quantity and convenience would be advantages.
Cost In economic times such as these the dollar can rule the recreation activities. Money spent traveling is better than that spent on the trailer parked in the driveway. A trailer with options to be added later, or as needed might be a good option. Buy the bare bones and add to it in time rather than taking out a thirty year mortgage.
There should be some consideration for the KISS offroad trailer. Simple is many times best. Also some consideration of the Glamper. Sure not everyone will pull the "Taj Mahal" or even afford it, but they sure are fun to ogle.
I also agree that there would need to be different categories. Rock crawler to forest roads. Base camp to light cargo.
It will be fun to see what list you come up with.