The button styles provide a range of visual emphasis depending on the needs of the content.
The "Feature" button is intended for the most important calls-to-action on the page. As such, an effort should be made to limit the number of these on a single page to maintain a clear focus for the content.
Standard buttons are suited for general use such as in sidebars or the main content.
Utility buttons are for controls that don't need to be visually prominent.
Arrow links are just a fancy link for use as a more subtle call to action in sidebars.