It would be the Angus breed.
The Holstein breed.
Angus cattle are the most common.
Merinos
There are no 'breeds' of chinchilla, but the most common colour is a standard grey
I know the American Shorthair is a pretty common cat, but it might not be the MOST common. :)
mutt breed cats are most common but after that is the tabby cat
Broad-Breasted White turkey is the most common.
Adelie and Emperor penguins are the most common to breed on the Antarctic continent.
i am obese too.
The Holstein.
The most common breed of dogs are Labradors. They are highly intelligent, very active, easy to train and they make a great family pet. I would recommend buying one!