Our first experience on the Queen Mary 2 taught us to check out what the balcony looks like on a ship before booking the stateroom. The QM2's balcony on the lower deck is cut out of the hull. While you can stand out on the deck and get the fresh air and sunshine, if you sit in the chairs provided, you can't see over the railing. Other decks have balconies with the familiar plexiglass that allows you to see through it. Now if you are going transatlantic on the QM2, you won't be using the balcony much anyway. It is too breezy and usually too chilly to be out there long.
I thought we had gotten wiser but then we booked a mini suite on a Princess ship and discovered that the newly designed ships are tiered. Therefore while you have a very large balcony, the two decks above you look down on whatever you are doing out there. So much for a cozy breakfast on the balcony.
There are some other balconies you want to watch out for. If it's privacy you want, be careful of what stateroom you book on the large RC ships, Allure and Oasis of the Seas. Balconies on most ships face out to the water and unless you are in port with another ship docked across from you, you usually have plenty of privacy. On the two large RC ships, there are some rooms with balconies that overlook the center of the ship where the park and other themed sections are. They may not be as private but they could be entertaining.
If you are booking through a travel agent, be sure to express your concerns and preferences. TAs will have a good idea of the layout of the ship. Most of them get to tour the new ships when they first come out or at least have a source to check the stateroom out. If you are booking online, check with some of the forums like Cruise Critic to see what you room might really be like. Some cruisers will even tell you if the location on the ship is good with regards to vibrations, elevators, etc.
Now, if your purse is up to it, you can get a balcony with a hot tub! We stayed next to the luxury suite once. We were a little stateroom tucked between two suites. That's as close as we'll get to the big suites unless we win a