I don't think there are any "bad" cabins on those two decks, so I think you should weigh the location of the available cabins on each deck much more than trying to figure out which deck. Ideally, you should look for proximity to activities that your family will be most interested in and to stairs/elevators. Also, if someone in your family is prone to seasickness, you may want to find a cabin toward the center of the ship, rather than forward or aft, to minimize the rocking motion.