On the new Celebrity Solstice, cruisers dine in a barrel-vaulted Tuscan steak restaurant divined by superstar designer Adam D. Tihany, watch glass-art vases as they are blown at the Corning Museum's hot glass shows and walk barefoot in the grass -- literally.

Aboard Holland America's new Eurodam, they find fresh orchids in the atrium bar, spend the day in a private cabana overlooking the pool and sip Flirtinis on a low banquette in the sultry Silk Den lounge.

On the Azamara Journey, guests take tea each afternoon in their cabins from a butler whose cart carries fruit tarts, delicate egg sandwiches with cut crusts and a half-dozen teas.

And when burger mania strikes aboard one of Oceania's ships, passengers have their choice of black Angus sirloin patties topped with jalapeño cheddar and sautéed onions; provolone, roasted peppers and pesto; or -- Oceania president Frank del Rio's favorite -- braised short-rib beef and crumbled blue cheese.

All four companies -- Oceania Cruises, Holland America Line, Celebrity Cruises and sister company Azamara Cruises -- fall into a growing class of ships that experts often describe as ''premium.'' Though these ships don't have the intimacy or extras of true luxury ships -- such as lectures from former secretaries of state and fine wines included with every meal -- they do offer substantive upgrades over ''contemporary-class'' lines like Carnival, Royal Caribbean and NCL.

UK-based industry watcher Tony Peisley likens the categories of luxury, premium and contemporary to the hotel star-rating system. But with cruise ships, it's not just facilities, service and dining that matter; it's also the density -- the ratio of space to passenger. Luxury are the least crowded; contemporary the most. Premium, he says, fall in the middle.

And premium upgrades extend far beyond duvets and flat-screen TVs, found on all newer cruise ships. Carolyn Spence Brown, editor of the bible of cruise sites, CruiseCritic.com, describes premium cruising like this:

''What you should get is upgraded dining, more sophisticated dining options, interesting shore tours or enrichment. And you should get more refined service.'' Decor and entertainment typically are more subtle than on contemporary ships. ''You're less likely to find reggae on deck,'' she says.

Itineraries are more adventurous, ship size is often smaller, dining choices decidely gourmet. Robes and upscale bath amenities are standard. The average age skews to Baby Boomers and older; on two of these lines, children are discouraged.

And while these cruises usually cost more than those on contemporary brands, the price is typically half that of luxury lines like Regent Seven Seas, Crystal, Seabourn and Silversea -- a definite factor this year not only because of the actual cost, but the perception, says Tom Baker, president of CruiseCenter.com, recognized by Conde Nast Traveler as one of the nation's top cruise agencies.

''It's not the most fashionable era to be spending that type of money,'' says Baker. Many of his millionaire clients, ``are buying down.''

Just which lines qualify as ''premium'' is a matter of debate among experts. Some argue that larger liners like those from Celebrity and Holland America can't compete with the 700-passenger ships runs by Oceania and Azamara. For some, the onboard experience on Princess ships is as good or better than that on Holland America, though the Princess ships typically are larger. And what about specialty ships like the breezy, 100-passenger ''yachts'' of SeaDream, and the tall-masted sailing ships of Windstar and Clipper?

The debate points to one of cruising's enduring and most maddening truths: It's not just the cruise line that shapes your experience, but the particular ship. After all, some newer contemporary ships offer butler service, a suites-only pool and concierge lounges.

That's where websites like CruiseCritic.com, blogs like USA Today's Cruise Log, online forums like the one at MiamiHerald.com/cruises, and experienced travel agents come in.

''The differences between the ships are so great,'' says Stewart Chiron, a cruise expert and broker. ``It's more complicated than just buying an airline ticket from Miami to L.A.''

OCEANIA CRUISES

Widely hailed for its superior dining and country-club ambience -- you'll find no formal nights on board -- Oceania Cruises has three identical ships, Insignia, Regatta and Nautica, each carrying about 700 passengers. Though the line is 6 years old, the ships are frequently refreshed and feel bright, almost new.

These boutique vessels feel like European country-house hotels at sea, with wood paneling and trims, rich golden drapes, carpets woven with Oriental patterns, color palettes favoring rose and royal blue. The result is decidedly upscale -- but not stuffy, says Cruise Critic's Brown.

''The little tweaks and touches are first-rate, things like Balinese beds on the sun deck,'' she says. Still, she adds, ``You almost don't remember the ship itself because the service is so fantastic and it's so much fun to be on board. There's great camaraderie.''

That's the idea, says Del Rio. 'Our ships aren't the `most' of anything. They offer a combination of warmth, service levels and intriguing itineraries.'' Those include sailings lasting from 10 to 40 days to ports including Egypt, India, Vietnam, Europe, Australia, Latin America and Caribbean mainstays including Key West. Itineraries sometimes call for more than a single night in a popular port -- a hit with cruisers.

Dining is a focal point -- and with the exception of wines, all meals are included in the base cruise fare. Menus here were crafted by super chef Jacques Pepin, with open seating in the main dining room (think blue corn-crusted duck appetizer and jumbo scallops in papillote) and alternative venues: the 90-seat Toscana, with an Italian menu; the clubby, 96-seat Polo Grill, with first-rate steaks; plus casual Tapas on the Terrace and Waves.

Discounts are common on Oceania; each winter the line typically offers 2-for-1 cruise fares and free airfare even to foreign destinations for the coming year. Two new ships, slated for delivery in 2010 and 2011, will carry as many as 1,252 passengers, double occupancy.

The cuisine won praise from Miami banker Jose Valdes-Fauli, who usually sails on luxury lines but chose Oceania for its Greek Isles itinerary. ''The food was very good,'' he said of his trip last summer, though he was less impressed with the service. And the average age was well above his own mid-50s. Even in July, he said, ``We were the youngest people on the ship.''

Del Rio, Oceania's president, makes no apologies. ``We're not ashamed. We know who are target market is. The Geritol crowd is the largest single group in the U.S., with the most discretionary income. If you're under 40 and you come on our ship, it must be a mistake.''

AZAMARA CRUISES

This sister company to Celebrity Cruises was created less than two years ago, when a corporate transaction brought a pair of 700-passenger ships to the company. Like the Oceania ships, these vessels once belonged to defunct Renaissance Cruises, and the layout of these and Oceania's ships are nearly identical.

More than $20 million was poured into each vessel; children's areas were eliminated, the spa expanded, a martini bar added, artwork by Roy Lichtenstein and Donald Sultan hung on the walls. Decor is traditional yet cozy; public spaces feature fresh flowers and non-working fireplaces. The dress code is casual but smart; no tux required.

Though one expert described Azamara as ''an intimate version of Celebrity,'' the ambience on its ships is decidely lower key. Think bigger library, less disco. Cabaret-style shows and vocal performances are held in a lounge that feels like a hotel piano bar rather than in a theater. In other spaces, guests may sip cocktails while a pianist tickles the keys of the grand piano, or in the Prime C specialty restaurant, enjoy a harpist as they nibble on foie gras and osso bucco.

Oh yes, specialty restaurants. Azamara's identical ships, Journey and Quest, each feature two: Prime C, where gourmet preparations designed by acclaimed chef Jacques Van Staden (who now works in-house for Azamara and Celebrity) include inventive dishes of steak and seafood, and Aqualina, with a Mediterranean menu. Both are included in the cruise fare, along with dining in the main restaurant and the casual buffet. Dining is served on a come-as-want basis.

Stateroom amenities are a step above contemporary ships -- think bottled water, fresh flowers, Elemis toiletries. Each cabin comes with a butler who rolls the tea cart around in the afternoons, per request; otherwise, his role seems to be that of a regular cruise steward, say those who have sailed with the line. Guests in suites get more specialized service, more space -- and larger bathrooms. (Bathrooms in standard cabins are snug.)

Itineraries range from seven to 24 nights, sometimes including multiple nights in popular ports, with destinations from Asia to the Caribbean. A 14-day Mediterranean route from Istanbul drew Sue Ervin, a South Florida development officer, onboard last summer.

One of her favorite features: Crew members went on all ship-arranged excursions. ``You got to know the crew. You knew the guy who did the seating in the dining room, and he made sure you got to sit with people you knew and liked. But it was still very professional. I would rate it very highly.''

Though Azamara president Dan Hanrahan describes the age range as ''50-plus,'' that's sometimes more plus than 50, say Ervin and other cruisers. ''It's somebody who is an experienced traveler, looking more for the destination,'' says Hanrahan.

CELEBRITY CRUISES

Azamara's big sister, Celebrity, now 20 years old, is known for its cuisine. It's newest ship, Solstice, launched last fall, boasts four specialty restaurants -- one specifically for passengers who book spa-class cabins, bistro -- and a spectacular Old Hollywood-style, two-level main dining room with a massive wine tower.

Nearly everything about the 2,800-passenger Solstice has won raves, from the grass lawn on the top deck, to the frosty -- literally -- martini bar, glass-blowing show, shagadelic disco, wine-tasting room, a capella singers, oversized lime-color wingback chairs in the coffee bar, art installations and large children's area. Where else can you sit in a two-story lofted library and look out over a living tree suspended in a soaring atrium?

''I think it is the finest ship I have been on,'' says CruiseCenter.com's Baker.

All these amenities come with a price: Size. With traditional cruise features -- formal nights and set seatings in the main dining room -- and a capacity of 2,800 passengers at double occupancy, can a ship really provide premium service?

Some experts argue no. But passengers seem to be happy, and even in this economy, Celebrity Solstice is sailing near full -- and getting a higher price than other Celebrity ships, say travel agents.

''We just loved it,'' says Sheila Nadell of Miami. She and her husband, Alan, have sailed with Celebrity 44 times. ``The service was great, the dining rooms were gorgeous. It had wonderful music -- not as stuffy as it sometimes is.''

Still, the Nadells say they prefer the smaller size of Celebrity's Century, which carries 1,800.

For passengers -- even those familiar with Celebrity -- knowing which ship to choose can be challenging. Like Holland America, Celebrity has a sizable fleet -- nine ships -- and size, style and amenities vary. Though most ships carry 2,000 passengers or more, Celebrity Xpedition -- which sails the Galapagos islands -- carries only 92.

What remains constant: High-quality art collections, fine dining and an active, sophisticated ambience that's a hit with the 45-60 set.

HOLLAND AMERICA

Founded in 1873, Holland America retains an air of maritime tradition, and even on its newest ship, Eurodam, you'll find ship models and maritime paintings mixed in with more contemporary touches.

For many cruisers -- even college student Becky Holtrop of Michigan -- the ambience is part of the appeal. ``I like the traditional feeling. I guess it depends on your personality.''

Holland America also clings to the idea that smaller is better, so while its ships have grown in size over the years, the largest still holds only 2,100 passengers at double occupancy. That medium size -- far smaller than the largest contemporary ships, which hold up 5,400 -- suits Miami passenger Karen Leibowitz, who sailed with Holland America to both Canada and the Black Sea. ``We prefer it to tiny ships because there's more to do.''

She also preferred the lines' beyond-the-typical sailings. Holland America ships offer hundreds of itineraries ranging from familiar, seven-day Caribbean voyages to an 108-day world cruise.

Holland America' average passenger age is 57, and when schools are on holiday, the children's programs and play spaces are lively. But on other sailings, say experts, most passengers are past Social Security age, and the ships take on a quieter atmosphere. Dining is by assigned time, though diners can opt to ''stand by'' at other times. Several formal nights are held during each sailing.

With 14 ships ranging in size from 793 to 2,106 passengers, facilities and shipboard experience vary. To smooth the differences, the line instituted a $525 million Signature of Excellence program bringing new lounges, eateries, verandas and upgrades throughout its fleet; all enhancements should be completed by 2011. On all ships, most service staff is Asian, and many crew members have worked with the line for years.

That's an added attraction for Holtrop, who has taken 29 cruises with her family, 19 of them aboard Holland America. ``The staff remembers you, even four years later. It feels like home.''