Exception: Royal Caribbean and other cruise lines will also use sub categories to distinquish between how many occupants the cabin will sleep. Therefore a cabin that can sleep up to 4 people will be a different sub category from a cabin that sleeps only 2 people.
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.
Very few ships actually have cabins dedicated to solo travelers. These will have sleeping space for one and can be quite small. The studio cabins on select Norwegian ships are the most famous example of this: The 100-square-foot staterooms each contain a full-size bed, nifty lighting effects and a large round window that looks out into the corridor. If you are a solo traveler, you will want to price out the cost of a solo cabin (usually somewhat higher than the double-occupancy rate of a similarly sized stateroom) compared to the cost of paying the single supplement (an extra fee tacked on if there are not two people in a cabin; the price can come out to as much as double the regular rate) for a standard cabin. And book early, as solo cabins sell out quickly.
When it comes to choosing suite accommodations, it is best to figure out how much space you really need, what amenities are important to you and what you can afford to spend. Suites on most ships are often the first category to sell out, partly because there are fewer of them, and partly because they often offer extremely good value. For this reason, it is important to decide early what kind of suite you would like.