I did a lot of research on this very question prior to booking cabin 1688 (category D1, aft) on Explorer. All the feedback I got was quite positive! These are wonderful cabins. I have stayed in the aft corner cabins on Carnival's Destiny-class ships and they were the best cabins ever! No problems with noise, movement, or anything for that matter. The aft balconies are sooooo much larger than the side balconies. The view is incredible. You get the best of all worlds back there! Go for it!!!
I've always heard that the aft was more prone to movement and engine noise. We'll have to rethink this position next time we book a cabin. We always try to get the middle of a ship. (Of course, if the ship is very large, you do have longer to walk to the main areas.)