If you tend to get seasick, cabin location is really important. It is a question of engineering, really. The lower and more central you are in a ship, the less roll and sway you will feel. Even if you choose a balconied stateroom, choose the lowest level and the most midship one you can find. The higher decks and cabins at the very front (forward) or back (aft) of the ship will rock and roll the most.
Having a personal butler can be a wonderfully pampering experience, and some cruise lines include the butler service as part of your fare when you select a suite or "concierge level" cabin. Look carefully at the difference in the cruise fare, and decide if it is really worth it. Beyond that, look at the services that are offered; some cruise line butlers really do provide extra value. For instance, some can bring you room service from hard-to-get-into alternative restaurants, refill your mini-bar to personal specifications, and serve in-cabin meals course-by-course. Butlers can also unpack and repack your bags, draw rose-petal baths and assist you in preparing in-suite cocktail parties.
Exception: Carnival has several cabins which are classified as inside cabins but actually have a french glass door which allows light into the room (no balcony, but the door can be opened). Carnival also has some cabins that have a window, but because the window has an obstructed view (that means there is a railing or object in the way) it is listed as an inside cabin. Royal Caribbean has some cabins that have a window but look out over an inside promenade area. These are called "promenade staterooms".
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.