I'd been on the world's longest megaliner, Allure of the Seas, for two days shortly after it launched in 2011. As I rode a glass elevator up, up, up through the ship's expansive atrium, two women chatted about how much they loved the ship.

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"You know," one excitedly said, "I haven't even seen the ocean yet!"

To some, that might be the ultimate indictment of the new trend toward cruise ships such as the Allure, which could contain five Titanics. But for those women, sailing the Caribbean on a floating megalopolis (that atrium, named Central Park, boasts a tree-studded, football field-size glen with a meandering path) was perfect.

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I long ago decided that when you figure in the costs of lodging, food, and transportation, cruising is by far the most economical way to see the world in comfort — even with a family in tow. What's more, because cruise ships come in all shapes and sizes, if you scan the horizon long enough, you'll spot a vessel that's perfect for you.

Megaships

2,500 to 6,000 passengers

You should pay: From $79 to $155 per day inside; $129 to $170 per day ocean view

(Norwegian Breakaway, Queen Mary 2, Carnival Breeze, Disney Fantasy, Royal Princess)

The best news for vacationers is this: More cabins require more passengers, and given the current economy, that means megaship deals are getting easier to find. After reigning as one of the Caribbean's most expensive ships a year ago, Oasis of the Seas is down to just over $100 a night per person.

Target Travelers
"Families take over these cruises," says Carolyn Spencer Brown, editor of Cruise Critic (cruisecritic.com). "There's something for everyone."

Entertainment
In the 1980s I sailed on Royal Caribbean's upscale Song of Norway, and one night's featured entertainment was, no kidding, a guy playing the entire 1812 Overture on an accordion. Today's megaship features at least one Broadway-type theater — and a show to match: Royal Caribbean has been staging the musical Chicago, and a How to Train Your Dragon ice show while the Queen Mary 2 offers a domed star show created with NASA. For quieter pursuits, Holland America’s Eurodam has paintings by Dutch masters and the line’s Rotterdam features exact replicas of China’s famed terra cotta warriors.

Pools
Take your pick: You'll find at least two and as many as five.

Cabins
Even on the biggest ships, cabins aren't much larger than the one the Marx Brothers spilled out of in A Night at the Opera. But the days of little portholes are gone — in an outside cabin, chances are you'll enjoy a nice balcony or large windows. What’s more, Disney has given a new life to those formerly dingy inside cabins: On the cruise line’s newer Dream and Fantasy ships, above the bed you’ll find a “virtual porthole” with a high-definition screen behind it. Cameras mounted up on deck beam the outside view all day long, and the result is an uncanny sense of seeing a live through-the-glass view.  

Dining
You can still head to the formal dining room, but the biggest ships pride themselves on offering countless dining options, from sprawling buffets to poolside grills. You'll also find premium restaurants that offer a fine dining experience worthy of a big city — for a reasonable extra cost. The gourmet menu at the Disney Dream’s Remy Restaurant — yes, named after the rat in Ratatouille — will run you an extra $75, but it was created by 2-star Michelin chef Arnaud Lallement of Riems, France. At Holland America, all 15 ships have menus created by a “Culinary Council” that includes such chef/authors as Rudi Sodamin, David Burke, and Charlie Trotter.

Destinations
Because of their size, megaships largely stick to ports with big facilities — places like the Bahamas, Mexico and the Mediterranean.

Midsize Ships

1,000 to 2,500 passengers
You should pay: $60 to $114 per day inside; $64 to $143 per day ocean view

(Carnival Pride, Celebrity Summit, Noordam, Queen Elizabeth, Norwegian Sun, Crystal Serenity, Coral Princess)

Target Travelers
"These boats cater to the traveler who is interested in fine dining and service — not rock climbing at sea," says Clem Bason, president of the online travel service Hotwire. Before ships like the Oasis set sail, these were the megaships. Now they can be an excellent value for travelers who want to enjoy traditional cruise-ship amenities. "They're more cozy," adds Brown. "You get to know your bartender."

Some midsize ships enhance the experience even further by taking on fewer passengers: While many ships measuring just over 800 feet long will hold more than 2,000 guests, premium ships like Crystal Serenity will host just over half that many. That means a lot more crew attention for you (Once I walked onto the Serenity deck and a crewmember chirped, “Can I get you a deck chair, Mr. Newcott?”) — but it comes at a higher price. A cabin on premium midsize ships like Serenity begin at around $300 a day.

Entertainment
Everything's a tad smaller: Rather than a Times Square theater, the stage venue on a ship like Holland America's Noordam more resembles a good Las Vegas lounge.

Pools
You'll find more than one, but they can be small, and it's harder to escape the poolside games.

Cabins
Most of these ships, built before cabin balconies became hot in the 2000s, have added them.

Dining
In addition to the formal dining room, there are several eat-on-the-run spots. The Noordam's casual dining area is a typical buffet, though with tablecloths and linen napkins.

Destinations
Midsize ships can go almost anywhere, from Bora-Bora to the St. Lawrence River.

Miniships

Fewer than 1,200 passengers
You should pay: By Sea: $120 to $500 per day inside; $120 to $350 ocean view

By River: $200 to $350 per day all with river view

(Oceangoing: Ocean Princess, Seven Seas Navigator, Crystal Symphony, Seabourne Pride,  Rotterdam)

(River: Avalon Affinity, Viking Pride, Grand Circle River Aria, Vantage River Discovery II, Queen of the Mississippi)

Target Travelers
Sophisticated vacationers and couples enjoy the lack of hubbub on these ships. “They offer superior service, dining and accommodations,” says Bason. “They often have 1-to-1 crew-to-guest ratios [the Oasis of the Seas ratio is about 1 to 2.25].”

River ships are another type of small-boat option. For as little as $150 a day, you can ply the waterways of Europe, Asia and Africa on sleek craft via lines like Avalon, Grand Circle, Vantage or Viking River Cruises. In the United States, Blount Small Ship Adventures and American Cruise Line sail the nation’s great rivers for $300 to $570 a day. Moreso than with large ships, river boat lines often offer good deals on air-inclusive fares.

Entertainment
Oceangoing small ships have intimate theaters and cabaret-type shows. Riverboats often limit their entertainment to local performers — and in Vienna, Viking took us to a lovely Strauss concert at the Auersperg Palace. Most European river cruises include shore excursions in the price — a big savings over most ocean cruises. In Nuremburg, Grand Circle now includes a visit to Room 600, site of the Nazi War Crime trials.

Pools
Seagoing small ships often have one very nice pool; river ships will occasionally have a hot tub. But small-ship designers tell me those facilities primarily appeal to travelers at the brochure stage. “The only people who use the hot tubs,” a Rhine River captain told me, “are the crew.”

Cabins
Ocean miniships have standard-size cabins, and in recent years riverboat designers have found ways to make their tiny cabins seem larger. Mini-balconies with sliding glass doors help a lot, but over the course of a week you’ll definitely master a sideways shuffle. In a major breakthrough for river touring, Vantage has introduced cozy single cabins with a twin bed on its three newest ships—an option that eliminates the dreaded “single supplement” charge that can make traveling alone prohibitively expensive. Vantage now has the single cabins on three of its newest ships—and remains the only major European river cruise line to offer them.

Dining
Some of the world’s finest restaurants can be found on miniship ocean liners. The menus are breathtaking — and you’ll be treated as if you’re sitting at the captain’s table. Although the quality of small-ship food is improving, most older riverboats have kitchens that are roughly the size of a minivan interior. Your best bet: Wander ashore each night, seeking out the local restaurants and pubs where the neighbors have been eating, perhaps for centuries.

All prices are per person, per day.