We had members of a large group that stayed in the Roy Disney Suite (Midship, deck 8?, 9? I don't remember) and another on the same deck aft (the rest of us were on deck 2 by choice) on the Eastern (7 day) and there was virtually no difference. It did seem the midship was a bit more stable feeling when I was in there, but the occupants claimed it was an exceptionally smooth time (each time I was there!) and they were "thrown from their beds!" every night. Of course, they also complained that the wood was scratched in their room. The family that was just aft claimed there was no problem, and they could tell no difference between the rooms. They had no complaints and are booking the same room for this next cruise coming up.
The Eastern cruise does roll a bit more than the Western or Southern, but it is in the open sea more, too.