The Best Way to Load jQuery Library (with fallback)

gistfile1.html

//Load jQuery Library

<!-- Grab Google CDN's jQuery, with a protocol relative URL; fall back to local if offline -->
<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="js/ext/jquery-1.7.2.min.js"><\/script>')</script>

<!-- Grab Google CDN's jQuery UI, with a protocol relative URL; fall back to local if offline -->
<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jqueryui/1/jquery-ui.min.js"></script>
<script>window.jQuery.ui || document.write('<script src="js/ext/jquery-ui.min.js"><\/script>')</script>

//Load jQuery library using plain JavaScript


<script>
//Load jQuery library using plain JavaScript
(function(){
  var newscript = document.createElement('script');
     newscript.type = 'text/javascript';
     newscript.async = true;
     newscript.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js';
  (document.getElementsByTagName('head')[0]||document.getElementsByTagName('body')[0]).appendChild(newscript);
})();

(function () {
 
    function loadScript(url, callback) {
 
        var script = document.createElement("script")
        script.type = "text/javascript";
 
        if (script.readyState) { //IE
            script.onreadystatechange = function () {
                if (script.readyState == "loaded" || script.readyState == "complete") {
                    script.onreadystatechange = null;
                    callback();
                }
            };
        } else { //Others
            script.onload = function () {
                callback();
            };
        }
 
        script.src = url;
        document.getElementsByTagName("head")[0].appendChild(script);
    }
 
    loadScript("https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js", function () {
 
         //jQuery loaded
         console.log('jquery loaded');
 
    });
 
})();

</script>