My favorite is category 7 on deck 7. I like being close to the top of the ship, and I like being close to the aft balcony on deck 7. As far as the cabins, the only difference (other than price) between categories 5 and 6 is the deck. Category 5 is on deck 7, cat. 6's are on decks 5 and 6. There are category 7's on all three decks.
I like the category 7 rooms because they're cheaper than the others. The verandah is a bit enclosed, but open enough for me, and is a fair trade-off for the savings, in my opinion. The rooms themselves are the same as the cat. 5 and 6 rooms.