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.

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.”

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.”

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.”

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.

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