Front living room does not appeal to me as the ceiling is 3 feet closer to your head than the lower part of the trailer. That said since much time can be spent there depending on your life style it is going to tend to be less comfortable and noisier when running the AC than a rear living room. The further your AC unit is away from your head the less annoying it will be sort of like central air vs window AC at home.
As others have pointed out manufacturers aren't sticking with them for long. When you're in the bedroom most of your time is lying down and living room sitting up. Just makes more sense in my opinion to have the bedroom up top.
I've noticed visitors stop at the bathroom and don't go into the bedroom and bathroom noises and odors are further from your company with a rear living room.
Just my ideas.