I am really not sure. It's your opinion. But if I did have to say the most popular I would say Cheerios's. This is my opinion so please dont go against it. Thanks!
cheerios
fruit and cereal
Michigan
Michigan
WHEATIES
While it can be technically eaten any time of the day, oatmeal is most consumed during the breakfast period of the day.
There really isn't a "typical" American breakfast as many Americans have vastly varying habits and tastes, but American breakfasts most often consist of some kind of a cereal based dish or an egg-based dish. The most popular breakfast beverage is coffee.
Ireland eats the most cereal coming in at 15 pounds per person per year.
grand slam breakfast
The most popular French breakfast is the croissant. The next most popular is a baguette with butter and jam.
Nature's Path
Probably cereal - although I personally prefer toast - or a bacon sarnie !!