Stone, who has a poodle named Dusty Springfield, volunteered for the North Shore Animal League America after seeing images of pets stranded in the aftermath of hurricanes Katrina and Wilma, said The New York Dog and The Hollywood Dog magazines.
The 18-year-old British singer also recorded a public service announcement seeking support for the homeless pets of the Gulf Coast.
"Joss is a huge advocate for shelter dogs and it's not just talk," said Leslie Padgett, editor of the magazines. "This year, despite an incredibly hectic schedule, she went out of her way to help the dogs of Katrina and Wilma."
Hilton, a 24-year-old hotel heiress and star of "The Simple Life," was voted the world's worst celebrity dog owner.
"First she loses Tinkerbell, then she ditches her for a cuter dog, then replaces that dog with a ferret, then a kinkajou monkey and then, I gather, a goat," Padgett said in a statement. "Recently Tinkerbell was spotted back in Paris' arms. But how long will she be in favor this time?"
Stone narrowly edged out Ashley Olsen, who adopted a mixed-breed from the Animal Haven Shelter in New York. Tori Spelling, a pug owner who has "tirelessly campaigned" for the Much Love Animal Rescue in Los Angeles, placed third.
The voting took place over a three-month period among visitors to the Web sites thenydog.com and thehollywooddog.com. Results were released Friday. The results weren't scientifically representative of the magazines' readers.