RGN would be my first choice. The drawbacks to a folding neck are having to release from the 5th wheel each and every time you load/unload, unhook air and electric, lay that greasy plate down in dust and dirt. Then you pick it up and all that crap goes into the 5th wheel. Lots of climbing on/off the truck. They have their place loading certain kinds of equipment. Back in the day my first haul truck was a winch truck and a laydown trailer. Lots of work. When I finally got a hydraulic detach I wondered what in the world I had been doing farting around with that laydown. Hydraulic folding helps as mine was drug up with a winch. One thing that was handy with mine was I could laydown, back up to the rear of the trailer and run my winch line out to drag a dead machine on. If trailer slid it would only slide until it was dead tight to the tailboard of my truck.
A lot of repeated detaching with a folding neck will be hard on a 5th wheel. Trash throws off adjustment, occasionally gives a false latch which will get your attention!
RGN is all ground level, no grease and dirt. Less deck and steel to track over and keep up with. There are pivot points of both but the ones on an RGN see less wear and stress when everything is in transport (supported) position. Usually folding necks have power unit in rear which means longer hydraulic lines to have issues with or if run by wetkit very long lines off truck and two more things to unhook.
I'm sure I'm overlooking other things but that's a start. Unless the laydown was dirt cheap and in good shape I'd go RGN. I've got a dandy Kalyn RGN I need to get finished up and sold....one of many projects lol