On [HTML5 Boilerplate][1] they use this code for jQuery:

    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
    <script>window.jQuery || document.write('<script src="js/libs/jquery-...

What's more readable:

    if (!window.jQuery) document.write(...);

or

    window.jQuery || document.write(...);

  [1]: https://github.com/h5bp/html5-boilerplate