Slight possibility of feeling some more motion the higher you go, especially if you get rooms towards the front, and sometimes way in the back. Only matters if you get motion sickness. Choose a room in the middle of the ship and low for the least motion. Otherwise, if you like being rocked to sleep, high and forward.
The rooms, amenities, and treatment are all exactly the same. I believe the only reason prices change is perceived value because on older ships you were closer to all the action on the top floors and had to use the elevators an stairs less.
Newer ships have the dining and show rooms in the lower levels so not a much advantage on the larger ships. Somewhere in the middle is probably best. Newer ships put their suites around the 6th level so I would guess that would be the sweet spot of the ship (pun intended). Most people recommend a room between to cabin floors because of less noise from public areas above and below.
To get the most "value" for your money pick the highest deck, but a room in the middle is more convenient to all area of the ship unless you have a preference to be closer to topside, or the interior. I doubt in the long run that it makes any difference to how much you will enjoy your cruise.