It's really not as simple as higher=better.
On Dream/Fantasy, the highest deck with cabins is deck 10. These are also the priciest cabins in their respective categories (5A/4A). These cabins also sit directly below the pool deck and if you do a search some people complain that the noise from above is a negative.
My preference is to have cabins above and below me. The odds of hearing noise are minimized (although not eliminated).
Then you have to think about where you will be spending your time on the ship. Midship usually has the least motion
if your cruise has much motion at all. I can promise you that if your weather is bad it won't matter where you are, you will be aware that you are on a ship. I love the idea of an Aft Balcony but probably would book midship given the choice.
Some people don't want to be near the elevators and vestibules. I have been directly adjacent (as in THE DOOR you see when you go into the hallway from the the stairwell) and had ZERO noise problems. That made it really easy for my child to find our room-as long as she got to deck 7 on the midship elevator, she could get back to the room if she needed to.
One person's ideal cabin is another's nightmare, and each sailing is different in terms of weather/headcount/the passengers themselves. If there are 1100 children on a given sailing I can promise you that things will be different from a week where there are 350.
Then you have to decide if bumping to a Cat 4 (the larger veranda cabin) is worth the difference in cost. I will tell you that 3 people can make it work in a Cat 5 but if we were 4 people we would absolutely book a Cat 4 cabin.
Our ideal cabin is a 5C, Starboard side for a view of
Castaway Cay. Somewhere between 7570 and 7580. We will see what our VGT assignment is for our upcoming January trip, and if we get a Cat 4 that is great, but I honestly would pick deck 7 over any other if I was booking a specific category.