On many ships, basic inside and outside cabins are usually the same size, the difference being that one has a porthole or picture window to let in natural light. Balcony cabins can also be the same size as standard insides and outsides, with the addition of the outdoor space on the verandah; sometimes the interior space is larger. A basic cabin, regardless of category, is referred to as a "standard" unless there is something about it that makes it different (such as physical layout, being handicapped accessible or a designated family cabin). With minisuites on up, you get bigger and bigger indoor and outdoor spaces.
If scenery is important to you, take a good look at your cruise itinerary before selecting your cabin, specifically if you are choosing an outside or balcony. On a roundtrip Caribbean cruise or a transatlantic crossing, for example, the side of the ship you are on does not really matter. If, on the other hand, you are doing a one-way sailing (such as a southbound Alaska cruise or a trip from Barcelona to Rome), you might want to consider choosing a cabin on the side of the ship that faces the land. Sometimes the views can be breathtaking, and you would not get those views from the cabins that face out to the open sea.
Do you need a balcony? Cruise travelers who spend all their time in the public areas -- sun decks, lounges, restaurants -- or on shore may be perfectly happy with standard-size cabins and no private outdoor space. Those who love to avoid the crowds and lounge quietly on their own verandahs or have private room-service meals outdoors will surely want balconies. Do not forget to take your itinerary into account; on a chilly-weather cruise, you might not be spending too much time outside, so depending on how much space and light you need, a balcony might not be worth the splurge.
Do you have to have a whirlpool bathtub or a walk-in closet? Will you be entertaining and thus in need of a dining table that can seat six or eight? Do you want benefits like priority dinner reservations and being first in line to get on or off the ship? Do you want to be pampered with extra-plush linens and bathrobes, fancy bath products and in-suite coffee and booze? You can find those amenities and more in most of the upper-level suites.