Strange that this question should pop-up. I just got off the Mariner yesterday and I was in cabin 6218 which is the third cabin from the closes cabin in the front. We had 20 ft. swells and it's was the most motion I felt since I can remember. I paid particular attention as I walked from the front of the ship to the back and I couldn't tell the difference in the movement of the ship. I now believe it doesn't really matter what location your cabin is. I've had cabins almost every where and if the water is rough (90% of the time it hasn't for been for me) you're going to feel it. I don't think you'll have any problems.
Sonny