There's nothing like having a baby sea lion burp in your face. And that's just what this one is doing — swooping up underwater to blow a bubble right at me, then stopping with its nose just inches from mine as if to say, "Your turn." Of course, I could've picked a more polite species of playmate (one of those busy mockingbirds who lands on your head) or even a more laid-back one (maybe a sleepy-eyed marine iguana). The wildlife on the Galápagos Islands isn't just fearless, it's got personality.

Meeting these characters, though, means traveling around the 80-odd volcanic islands, 600 miles off the coast of Ecuador. And with just two airports in the whole archipelago, the best (and only) way to go is on a live-aboard boat. More than 80 such vessels, carrying between six and 100 passengers and ranging from rustic sailboats to motor sailers and yachts to mini-ships, travel among the eight or nine most popular islands. But the boats don't all make the same stops or let you spend the same amount of time ashore, so you need to choose carefully.

First, consider what kind of Galápagos experience you want. Which islands you visit, what animals you see, and how much hiking and snorkeling you do is determined by your vessel. Small boats can slip into shallow harbors where big boats can't; big boats may have more on-board activities for less outdoorsy travelers. Guides, too, will affect your experience. Class III naturalists speak three languages and have at least a college degree in a life science; Class I guides may not even have a high-school diploma.

Then there are creature comforts. The boat will be your home for seven or eight days (shorter tours are hardly worth making the trip, since you spend two days in transit). Can you go for a week without a double bed or laundry service? Do you like aperitifs on the sundeck? Know, however, that none of the boats here has the amenities of a mainstream cruise ship, like pools and room service.

By law, only Ecuadoran boats can offer regular Galápagos cruises, so your U.S.-based outfitter won't own the boat or employ the captain and crew. Sometimes the outfitter doesn't directly employ the guides, either, or even have an office in Ecuador. If something goes wrong, you're dependent on the hired contractors — people who may or may not feel an obligation to help. So ask a lot of questions. The more specifics a company provides, the more you can usually rely on them out in the field.

Last year, I went to the Galápagos with three reputable, U.S.-based companies. Each offered Class III guides and a reasonable level of comfort (there were none of the on-deck showers or shared bathrooms you'll find on the very cheapest boats) for roughly the same price, but the trips — and experiences — were wildly different. Here are the results, to help you make your choice.

Living Large
Lindblad Special Expeditions is one of the surest bets you can make in the Galápagos — and the most comfortable. There's a trade-off, though, since better facilities mean a larger boat, and a larger boat means more time spent on logistics and less time spent at each island.

Like the three or four other large "ships" in the archipelago, SE's 80-passenger MS Polaris appeals to travelers who enjoy eating in a nice dining room as much as they enjoy spotting a short-eared owl. By Galápagos standards, these accommodations are luxurious. Most cabins have large windows (not portholes), two twin beds (and a maid to make them), and a real shower (not a hose attached to a sink). Dinners feature fresh lobster and grilled snapper with red-pepper coulis, and lunch is even better: buffets with Ecuadoran potato-cheese soup, fresh mangoes and watermelon, and seafood paella.

However, you simply can't interact with animals and their surroundings from a big boat the way you can from a small one. Let's say you're on Hood Island, hiking its 1.2-mile trail with 70 other people (which can be distracting even when you're split into groups): While you're watching the albatrosses do their mating dance, another group arrives, whispering and calling out.

Still, for a large boat, SE's Polaris gives you plenty of nature. The 424-volume library is stocked with guides to the stars and the birds, plus the requisite copies of Darwin's On the Origin of Species. (Small boats usually have only one shelf of books.) Though the guides — five Level II Ecuadorans and a Level III American biologist — individually seemed less well-informed than the guides on my two small-boat trips, their range of specialties almost made up for it.

Another (unexpected) benefit was privacy. In a group of, say, 10 travelers, you may feel you should join in every single activity from sunup to sundown. But with a group the size of SE's, nobody really notices if — for you — today's adventure is just curling up in a deck chair and watching the waves roll onto shore.

Contact:             800-397-3348      . Price: 10-day trips on the MS Polaris begin at $3,620 per person, double occupancy, for a lower-deck cabin. (Price includes all flights inside Ecuador; international airfare is extra.)

Sailor Suited
At the very worst, my trip with Mountain Travel-Sobek was an adventure (no showers), and at the very best it was . . . an adventure (petting reef sharks). Most of the best adventure was the result of being aboard a motor sailer, a sailboat with an engine that can power you to far-flung islands like Tower, home to hundreds of exotic seabirds. (Watch out, though. Some smaller motor sailers can't make it that far.)

Sobek's Diamant is particularly beautiful. It's a 112-foot schooner with six staterooms, teak and mahogany paneling, and brass carriage lamps. The cabins, however, vary dramatically and are assigned on a first-come, first-serve basis. Of two couples who paid the same fare, one might get a bunk-bed setup with a shower hose attached to the sink (standard on most small boats), while the other might draw a double bed with huge picture windows and sitting area.

The selling point of this trip, however, is what's outside — from wildlife viewing to snorkeling to impromptu swims off the deck (impossible on a large ship). Meals are served on a picnic table under the stars, family style. Most of them were simply prepared but fresh — papaya juice and pancakes for breakfast or, for dinner, grouper in cream sauce, salad, and baked apples for dessert.

Your trips to each island last at least three hours, giving you more time than some of the others do to find that fur seal huddling in a cave or lone flamingo napping in a lagoon. And with one Class III guide for the 10 of us, each person got more attention than on the Polaris and more say in our itinerary; one day we voted to detour to a lava tube instead of heading back to the boat.

Unfortunately, Sobek didn't have its own office or representatives in the Galápagos, and its two contractors, Quasar and ExplorerTours, made mistakes: People weren't met at the airport; luggage was lost, permanently; and — perhaps not surprising in a boat just out of dry dock — the Diamant 's air-conditioning and water-filtration systems broke down. To its credit, Sobek paid for the luggage and apologized profusely. The company's new Galápagos chief, Susanne Methvin, is revamping the program, using some of the best-managed boats (like the Letty and even the Reina Silvia — a motor yacht I took with another company) in the islands.

Contact:             800-282-8747      . Price: 11-day excursions begin at $3,573 per person, double occupancy, for the motor sailer; it's $3,395 for a motor yacht (including airfare inside Ecuador).

Tightship
I.N.C.A. manages to cram a fair degree of big-boat luxury into a small-boat trip; more importantly, its people know what they're doing. In fact, after watching the pre-trip video, reading the novel-length brochure, and speaking with one of their ultra-attentive reps, you too will feel like you know what you're doing. In fact, that's exactly what I.N.C.A.'s customers expect; most of them were savvy, demanding travelers with lots of travel experience. However, they could also be demanding in a difficult way; our group lacked the try-everything, whatever-happens-happens attitude of the Sobek passengers who, even if hesitant about, say, snorkeling, would try sea kayaking instead.

My boat was the Reina Silvia, a 16-passenger, 90-foot motor yacht that combined the best of the Polaris and the Diamant. Along with the feeling of being right on the water, the boat has beautifully decorated indoor spaces, including a tapestry-lined library (with VCR) and a dining room (pink linens, roses in bud vases, and a full bar). Other than the palatial sundeck suite, however, the cabins are typical sailboat-style bunks with bathrooms that convert into showers. The meal presentations were as elegant as on the Polaris, with waiters and a grand finale steak dinner, but the food was simpler. Dinners began with a soup, maybe spicy peanut or a corn chowder, continued with broiled chicken or fish, and ended with anything from bread pudding to yellow cake heaped with icing.

Where I.N.C.A. really shines is in its organization. The company charters the Reina Silvia but has its own guides and an office on the islands, and it sends anonymous evaluators to make sure trips are up to par. Our guide could do everything from describing the life cycle of a blue-footed booby and bringing up a sea cucumber from the ocean floor to pointing out all (and I mean all) the constellations in the sky. The only problem was that he sometimes forgot the "guiding" part of guiding — in his excitement over exposing us to new things, he'd leave less-confident swimmers or hikers behind.

Still, for an in-depth look at the Galápagos, you can't beat this trip. Our group (mostly 40- and 50-something executives from California) was introduced to nonagenarian Margret Wittmer, one of the founding settlers of the islands, and even got the chance to tour a private farm that just happens to be one of the last places on earth where you can see a 300-pound Galápagos tortoise lumber around outside a cage.

Contact:             510-420-1550      . Price: 11-day motor-yacht excursions start at $3,918 per person, double occupancy (including airfare within Ecuador). Motor-sailer trips begin at $3,818.