You probably can't describe the difference between Coke and Pepsi. Perhaps one cola seems sweeter, but you couldn't certainly distinguish them in a taste test. Yet you know without a doubt which one you like more.

The fierce brand loyalties of Coke vs. Pepsi are a marvel of American marketing.

Slightly older, Coca-Cola was always the dominant brand.

Pepsi gained market share in the middle of the century with a series of ad campaigns. In 1975 the first Pepsi Challenge claimed that people preferred Pepsi in a blind taste test. The brand was also marketed as the soda of the new generation, with celebrity spokespeople like Michael Jackson.

Today America's preference is firmly divided by demographics, according to research by Hunch.com. Surprisingly there's a big divide based on wealth and education.