The interior cabins are virtually all the same; I don't think you can single out a "best" or "worst". I think your guidline should be, "where do I plan to spend most of my time while onboard?"
If you plan to spend a lot of time around the pool and playing sports, then Lido Deck or Riviera Deck might suit you. On the other hand, if art auctions, the Casino, shows, card games, the library, classes and lectures are your thing, Dolphin Deck or Emerald might be for you. If you are looking for real economy, Plaza Deck is actually a very good location. Or, if you plan to do some of everything, Aloha, Baja or Caribe Decks would be a good compromise.
If you are considering a balcony, the same guidlines could apply. There are no bad balcony cabins; but if you would like a recommendation, I would suggest the Catagory BB Balcony Cabins on Caribe deck. All the balconies on Caribe Deck are larger than the other standard balcony cabins; and Catagory BB will save you a little money over Catagory AB. Or if you are lucky enough to snag one of the BB's aft, grab it!
Hope this helps a little.