Choosing a column class

This is a good question. With all of the class options, it can be hard to decide which ones to use. If you are building a mobile app, then you would likely want to stick to the extra small or small column classes. For a tablet, you might want to use medium. If the primary user for your application will be on a desktop computer, then use the large or extra large classes. But what if you are building a responsive website and you need to target multiple devices? If that is the case, I usually recommend using either the medium or large column classes. Then you can adjust to use larger or smaller classes where necessary if you have a component that needs some extra attention for specific resolutions.