Around here, in rural AZ, if you say beans, it is automatically assumed you mean pinto beans. If you don't mean pinto beans, you need to say what kind of beans you are talking about. Green beans or string beans, could also be pintos, but at a different stage of growth. A can of beans could be kidney beans or navy beans, but if you are talking about dry beans, and you want to tell someone about eating beans, you don't have to ever say I ate a bunch of pinto beans.
Pinto beans have always been available in local grocery stores in 50 lb. bags, but that was the only such bean until very recently when the hispanic stores started carrying a few bags of black and peruano beans.
Health food stores, thanks to vegetarians, now carry a lot of different beans that have never been available in regular grocery stores. Adzuki beans, for instance, and a whole bunch of different varieties of lentils and soybeans.
I like to try them all, to see what they taste like, but fall back on pintos as the bean my family most often ate when I was growing up. They were always served on roundup and in steakhouses, and were the favored method for getting through times when cattle prices were down, in the days prior to food stamps. Pinto beans were used as poker chips, in a few famous instances where one bean represented one cow and whole herds were lost or won over a night of playing cards. I know it's different in different regions of the country, but around here pintos are far and away the king of beans.