title: Choosing application server for API backend
body: <p>With so many choices for the application server (Passenger, Thin, Unicorn, Mongrel, Puma and Rainbows!), I'm wondering what would be appropriate for the following scenario:</p>
  
  <p>Rails is used purely for API backend (all assets are served with Nginx). Some of the API calls rely on other API services, so sometimes they take a while to finish.</p>
  
  <p>The responsive app is used with mobile, tablet and desktop clients, so there's no guarantees about the client's connection.</p>
  
  <p>What application server do you think is appropriate in this case? What things should be considered when choosing?</p>