The trailer I use must now days is a 20'lowboy rated for 10k. I use 4' ladder ramps with no support legs.
I prefer these simple ramps because;
A. I load and unload on all kinds of surface,many times unlevel. Supports can hang up on these surfaces.
B. I often haul tractors with mower attached. Mower overhang's rear because tractor isn't all the way forward on trailer when weight is balanced so hinged ramps would be in the way.
C. Ramps with supports are too heavy to lift into transport position unless they have spring assist and springs have a way of breaking at the worst times.
D. Ramps are always too short for low center things like cars and a workaround with support ramps is all but impossible. I can put trailer wheels in a low place or back up to street curb making it easy with ladders. I have a basket of 2Xs,4Xs and blocks outside cargo space between fender and front of trailer. If I load something heavy like the 9k Lb 4020 Deere,I simply throw blocks under rear of trailer and center of ramps. When I had construction equipment,I had dedicated trailers with hinged ramps. Personal preference according to purpose.