Bitter is a serif font. It goes well with Open Sans, Work Sans, Helvetica Neue, Source Sans Pro and Gotham. If you're thinking about using Bitter then try 26px for headers. Give 20px a shot for content.
People commonly tag it as design, blog, writing, fashion, agency, app, marketing, portfolio, slab serif and modern. You can get it from Font Squirrel, Google Web Fonts and Typekit.