What is the most common breed of domestic duck?

The most common breed of domestic duck is the Pekin duck, especially in commercial meat production.

Pekin ducks descend from domesticated mallards developed in China. Ducks from China were brought to the United States in the nineteenth century, where American breeders selected the familiar large-bodied, white-feathered form now called the American Pekin. The breed is valued for rapid growth, plentiful meat, and a generally calm temperament.

Pekin ducks became central to commercial duck farming in the United States and remain the predominant breed in worldwide commercial production. Their white plumage also makes processing easier because it leaves a cleaner-looking carcass than darker-feathered breeds. “Pekin” and “Peking” are related names, although Peking duck can also refer to the famous Chinese dish rather than the living breed.

Mallards are the wild ancestors of most domestic duck breeds, not usually the answer to this question. Muscovy ducks belong to a different genus, while Indian Runners are especially noted for egg production and upright posture rather than overall commercial dominance.