We've had a Cat. 6, 8 and 10 (all on Deck 6) for our family of 4. We felt the balcony was a waste of money, as we spent almost no time on it. The category 10 wasn't bad, but we enjoyed the 8 more. The big round window let in lots of light, and the sill was deep enough for my kids to use it as a seat.
We originally booked a Cat. 10 for our Eastbound Panama Canal cruise in August because the cruise is so expensive; reconsidered, and we are now waitlisted for a Category 9 for not a lot more money. It has the same big window as the 8, but I guess will be on Deck 1 or 2.
If I were in your shoes, I would look at booking 2 Cat. 9s if you don't mind being on Decks 1 or 2. You'll have double the bathrooms and storage space.
Remember that the first 2 passengers per cabin pay adult fare, regardless of age. If you've been counting on two adult fares and three child fares, you might be better off with the Category 4.
It's late -- does any of that make sense??
Karen
Wonder 11/01
Magic 3/02
Magic 11/02
Carnival Destiny (don't ask) 12/03
Booked on Magic Eastbound Panama Canal 8/05