With our family we prefer to be up higher rather than lower. This gives easy access to the outdoor recreation areas, fitness center, and windjammer cafe without getting on an elevator. also the view is better when in port as you have less chance of being blocked by structures or other ships. While we haven't been on the FotS, it seems the deck plans still support this view.
I would only pick the lower cabin if:
1) I planned on spending most of my time inside
2) got motion sickness as the pitch and roll would be slightly less if down low.
I didn't like the rear of the ship on Deck 7 on the JotS as we got noise from the Safari Club in the evening. This wouldn't be an issue on Freedom as deck 6 has cabins below. I doubt the vibration would be bad in the back as the propulsion system on Freedom uses the modern pod system.