title: When creating service method what's the difference between module.service and module.factory
body: <p>I don't know what is the best practice and what I should use.</p>
  
  <p>What is the difference between below two methods?</p>
  
  <pre><code>module.service(..);
  </code></pre>
  
  <p>and </p>
  
  <pre><code>module.factory(..);
  </code></pre>