My personal favorite bean, they are lighter in color, creamier in texture and softer than black beans. In Northern states, the pinto is the most popular bean.
In Sinaloa they cook them with onion, garlic, tomato and the serrano chile, those four ingredients that are the basis for many Mexican dishes. There is also a twist on Sinaloa beans called frijoles puercos or piggy style beans which is rather heavy, and served with bacon, chorizo, and cheese. It is delicious!!! (continue for more information and a photo).
Known for its mottled skin, it is also the most common bean in the US.