My opinion for what it's worth...

The lower the cabin, the less movement you feel, the more midship, the less movement you feel. Therefore, if you have any type of queesiness related to rocking ships, you will be happier on a lower deck.

On the Voyager, I love the most basic rooms. I think the G rooms are the best because they are convenient to everything and are very private.

On the Mariner, I tend to like the higher floors because they have a laundry room on the halls. On this ship, I like the Penthouse suites (C class) the best. I would opt for the larger room on a long trip.