Los Angeles — Help wanted: One trained, easygoing, low-maintenance dog that will work for next to nothing. It was the classified ad that Matthew VanFossan wrote in his head after going blind.

His Labrador retriever, Achilles, "will guide me across busy streets for nothing more than a pat on the head or 'Good boy,'" said the 31-year-old writer-counselor from Los Angeles. "He loves every bit of attention, but he can also go without it. He'll let out a low groan if he's getting too bored."

The breed's friendliness, intelligence and love of physical activity helped make it the most popular dog in America for the last two decades, according to American Kennel Club data released last week. Labrador retrievers are widely used as search and rescue, guide, therapy and service dogs, and they're also perfect for active, outdoors-loving families with children, said club spokeswoman Lisa Peterson.

Labrador retrievers (22 years), cocker spaniels (23) and poodles (22) have been the most popular purebred dog breeds in the United States for a total of 67 of the 128 years the AKC has been counting. The data from the AKC, the country's only nonprofit dog registry, comes from paid registrations by breeders and owners of purebred dogs, and makes the dog eligible for AKC events such as dog shows. More than 40 million purebred dogs have been registered since 1884, Peterson said.

Some critics, like the American Society for the Prevention of Cruelty to Animals and the Humane Society of the United States, argue that owners mistake club registration as a sign of responsible breeding. "Registry with the AKC simply indicates that a dog had two parents of the same breed," said Cori Menkin, senior director of ASPCA's Puppy Mills Campaign. Menkin added that breed popularity can often yield breeders who are trying to meet public demand and don't care about inbreeding or humane conditions.

The AKC acknowledged that registration does not guarantee the quality or health of a dog but condemned irresponsible breeders.

Factors, including Hollywood, pop culture and the economy, help drive changes in breed popularity. For instance, the yellow Lab featured in the bestselling memoir and the subsequent movie "Marley & Me," help the breed's popularity skyrocket, Peterson said.

Likewise, the popularity of other breeds has soared thanks to the beagle Snoopy in Charles Schulz's Peanuts comics, "Lassie" for collies, and cocker spaniels from "Lady and the Tramp." Snoopy has been one of the biggest influences, Peterson said, and is the only non-dog to be issued an AKC registration certificate.

But "the No. 1 thing that drives changes in dog popularity is people's lifestyles," Peterson said. In New York City last year, larger breeds such as the Labrador retriever and German shepherd jumped over the smaller Yorkshire terrier. Peterson attributed to the economic recovery, saying "people are going back to larger dogs."

The short-haired dogs are easier to groom, easier to walk and to exercise than the smaller, more time-intensive dogs, she said. She believes smaller dogs became popular because of the recession because that trend started in the 1990s.

Another popular breed, the cocker spaniel, has owners coming back for its friendliness. Carol Bryant, a blogger from Forty Fort, Pa., travels frequently and uses her cocker spaniel Dexter as a networking tool. Dexter is so good that he has his own business cards, she said.

Of the breeds that made most gains in popularity, the most noticeable has been the bulldog, said Peterson. It has inched up the last five years, most recently to No. 5 nationally in 2012, she said.

She attributed some of that to "great visibility. It's the mascot for the U.S. Marines. Think of all the colleges that have bulldog mascots. The Mack truck has a bulldog on the hood. And Tillman and Beefy are real bulldogs who skateboard."

Celebrities such as Brad Pitt, rapper Ice-T and athletes Michael Phelps and Sean White, have bulldogs, she added, which could partly explain why the breed is No. 1 in celebrity-driven Los Angeles and Las Vegas.

Bulldogs "have such great temperaments, they are adorable puppies, they are sturdy and compact, and they have the wrinkles and the eyes. They don't require a lot of grooming or exercise and they love to stay in the house and be with you or if you like the outdoors, they love that too," Peterson said.

The small, sturdy breed also is compatible with owners of all ages, she added, making it ideal for multi-generational families. That comes in handy as the economy forces more adult children to return home.

When it comes to America's top dog for the past 20 years, practicality beat being fashionable. The Labrador retriever's intelligence earned high marks among owners who sought out the breed.

VanFossan, who lost sight in both eyes by age 22, has owned two Labs. He tried using a cane for six awkward months, then got a guide dog — a Lab named Gilly. Their time together became a book in January — "Through Gilly's Eyes: Memoirs of a Guide Dog" — and his second dog is Achilles.

"Achilles is a little more sensitive but is better at remembering. It's incredible. I can go to a new place just once or twice, and he'll have the route memorized. Sensitivity has its advantages," VanFossan said.

Linda Markley, a mother of three in Los Angeles, returned to the breed after her first Lab — a shelter find — died. When the rescues turned up none, she went to a breeder to buy Riley.

Markley said she loves Riley for dozens of reasons, but is most impressed with her memory for human vocabulary and street smarts. She knows words like "keys," ''shoes," ''park," and "shake," and can understand phrases such as "go to Ryan's room," ''go to Jack's house," and "let's go for a hike," the proud owner said.

And Markley has no doubt that Riley understands what she's saying: "She loves sticks, so she doesn't chase balls or swim in the pool. If you say, 'Do you want to go in the water?' she will run the other way."