I had a lower bunk my third class year. In port one night I woke up one night with something dripping on my feet. The second class deckie was in his middle bunk drunk and throwing up. He got his bumk the one under him the two infront of his and the four on the side of his. 3 oclock in the morning and I had to head to the showers. I left him being taken care of by his classmates.
On the Coast Starlight trains that run between Seattle and Los Angeles, the upper berths have no windows, which makes it slightly less interesting before you actually do fall asleep.
Helping a fat drunken sailor with puke on him into his top rack is not fun.
Top rack is also at eye level, meaning if you want ‘private time’, you risk being seen if there are any gaps in your curtain.
The top rack also had no enclosed top, so light poured in. Bottom/middle racks you could double curtain and get nearly pitch black even if the berthing lights were on.
Top rack was also closer to the noise from the compartment above. I remember one thankfully brief period when I was temporarily in a berthing under the flight deck, directly underneath the middle of the #3 arresting wire, meaning 50 ton aircraft were undergoaing controlled crash landings 4 feet above my head. Not restful. The bottom racks weren’t much better but every little bit helps.
Only benefit to the top rack was more head room.
Most of these are rather unique to the navy, ofc.
No experience with this myself, but I would think the problem with lower berths that had been used as benches would be: Possibly smells like ass, stuff spilled on them, crumbs, etc.
On the Superliners (which constitute most if not all of the sleepers in the western US), the view from the lower berth in a roomette ain’t all that hot either — the lower edge of the window is 8" or so above the berth level. You can see the stars, though.