I've seen this all my cruising life, but I'm not sure...: Mid Ship as low as you can get is "supposed" to be the best area to not get seasick.
Considering how big and how stable ship's are these day's, I really don't think it makes a lot of difference .
If I was prone to motion sickness, I'd skip the cabin's that are very forward and those very aft.
Well, according to the laws of physics a ship can move three ways about three axes. It is best in each case to be nearest the center of gravity of the ship to minimize motion. That means midships, normally on a low deck (but not the very lowest decks which are usually not passenger decks anyhow) and in fact, in the center of the ship instead of an outside cabin. That's science.
BUT -- as has been said, modern ships are so big and so well stabilized that it really seems to make very little difference. If it really were a critical factor, the ships would put their dining room at that central point of least motion, wouldn't they? Yet none of them do.
Personally we are very happy with a balcony cabin far forward on a high deck. But if it is a real concern get that nice inside cabin on deck 4 and save a bunch of money!
Good point about the dining rooms, & buffets are usually at one end or the other. We personally love aft cabins if we can get one, never noticed any movement that much, you do get noise when docking & a long walk to anywhere. I have found that old cruisers go for location & ease of access rather than having a so called better cabin.
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