When you book a guaranteed cabin in any category,you need to check the ships deck plans and make sure that you can live with ANY cabin in that Cat. If you have any doubts, then it's wise to fork over the extra $$ and select the cabin you want. You might end up with a wonderful cabin but might also get one with an obstructed view or be under the disco. It's a crap shoot. Are you in the U.K? Not sure how the booking process works there but here in North America, (on my line of choice, which isn't RCCL) a guaranteed balcony price is the same as the lowest balcony cat. so you can select your cabin for the same price as a guarantee.
Whatever you decide, I'm sure it will all be good-have a great cruise! You'll be hooked