And don't forget the river ships, now every bit as luxurious as their ocean-going rivals, and those cruises with a cultural bent and expert lecturers on board. Here's our guide to choosing a cruise.
The destinations
When choosing a hotel the usual considerations are: Do I want to be by a beach or in a town or city, in a boutique property or large resort and do I want a room with a view and balcony or the cheapest accommodation because I won't be spending much time in the room? Selecting a cruise is no different.
Many of today's mega-ships are destinations in their own right, but being able to visit lots of different countries, parts of a region or islands on one holiday without the usual logistical hassle is still the main reason most people choose a cruise. Whether you are new to cruising or not the itinerary is a good place to start.
Cruising is often unfairly dismissed as unadventurous. Yet there are opportunities to join a cruise and go hiking in the remote Scottish Hebrides or rambling in Madeira; to learn to dive in the Caribbean, spot polar bears in Spitsbergen or camp on the ice in Antarctica.
Your destination choice will, to a large extent, dictate the size and style of cruise ship you pick. For instance, if adventure cruising appeals, you can expect to be on an older, smaller ship with a few hundred passengers plus naturalists, geologists and marine biologists.
If you want a family cruise (the industry body CLIA calculates that worldwide about 1.5 million youngsters aged 18 and under cruise each year), go for the resort-style vessels with multiple activities and dining venues.
Dressing up, or down?
These days, cruising can be as formal or as informal as you like and river cruises are much less formal. P&O and Cunard have formal nights, with black tie de rigueur in public areas on certain evenings. On other lines a jacket will suffice, and many have dropped dress codes altogether.
Choose with care if dressing up on holiday does not appeal, and you don't want assigned seating in the evening (where you are allocated a table and time to dine, often sharing with other people selected at random, for the duration of the cruise). Increasingly, cruise lines are offering open seating, allowing you to dine when and with whom you want.
Accommodation
You also need to decide what sort of cabin you'd like. Inside cabins (no window) are the cheapest, but you can pay a bit extra for a room with a sealed window. Cabins with balconies are the most popular, but if money is no object then suites are a treat - they're spacious and often come with a butler and little treats like a free minibar or pre-dinner canapes. Some companies cater especially well to singles who don't want to pay through the nose for a double cabin.
Consider the costs
Obviously price is important, but choosing a cruise only on cost could be a false economy if you don't have a good holiday. With entertainment, children's clubs and as much food as you can eat included in the price, not to mention fierce competition forcing prices down, there has never been a better time to book. Watch for deals when the lines try to secure early bookings. You can often also benefit from free flights, drinks-inclusive packages, upgrades and on-board credit to spend in the spa, bar and shops or on excursions.
Tipping
Most cruise lines put gratuities on the bill as a "per passenger per day" charge. One way to avoid the tipping is to book a cruise with one of the luxury lines, which include drinks and gratuities in the price.
