which is better orientation of the MBR on fifthwheel

A lot will depend on the length and weight that you want. Suggest that you go to some RV shows and spend time in some units. You can find a standard queen without a bed slide. We wanted to stay shorter and lighter, so we opted for a closet slide. The closet is not as big, but fine for us for our 4 to 8 week trips. We also liked the layout because we got real nightstands on both side of the bed. In the end, it was what could we access with slides in (like fridge).