Jersey
It would have to be the Holstein.
The Chihuahua is the most popular breed of toy dogs. The second most popular toy dog breed is the teacup yorkie.
Most of the cattle in NZ are Dairy cows, and Frisian is the most popular breed because of its good production quantity. (As measured by Milk Solids.) Jersey cows used to be the common dairy cows, but no longer. For Beef cattle, Angus would be among the most popular. Hereford are another popular beef breed.
The Quarter horse
This breed is a dairy cattle. The standard colour is black with white markings. They are popular for their large amount of milk production. The fat percentage is about 3.5%. The Holstein-Friesian is the most popular dairy cow in Australia.
The Golden/Syrian hamster is the most popular breed.
Jersey
Persians are the most popular cat breed, but most cats owned are mongrels (mixed breed).
The most popular breed is probably the Moggy which is just a normal cat with no particular breed.
Angus cattle are the most common of the beef breeds and Holstein cattle are the most common of the diary breeds.
The most popular cat breed right now is the Persian.
The Holstein, is, by far, the most popular dairy breed in the world. Holsteins go by other names due to influence from other breeds or the difference in language in other countries, but ultimately they are the same type of bovine that is very popular for producing vast quantities of milk per milking and per year.