backbone.js & underscore.js CDN recommendation?

http://www.cdnjs.com hosts a lot of less popular JavaScript frameworks, including:

backbone.js: //cdnjs.cloudflare.com/ajax/libs/backbone.js/1.0.0/backbone-min.js (HTTP | HTTPS)

underscore.js: //cdnjs.cloudflare.com/ajax/libs/underscore.js/1.5.2/underscore-min.js (HTTP | HTTPS)

For convenience, here are the script tags:

<script type="text/javascript"
   src="//cdnjs.cloudflare.com/ajax/libs/backbone.js/1.0.0/backbone-min.js"></script>

<script
   src="//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.5.2/underscore-min.js"></script>

http://www.jsdelivr.com/ is also a good alternative for less popular frameworks

backbone.js: //cdn.jsdelivr.net/backbonejs/0.9.10/backbone-min.js

underscore.js: //cdn.jsdelivr.net/underscorejs/1.4.3/underscore-min.js

Also in most cases it is a good idea to omit the protocol in the URL for JavaScript source.

More on http://www.paulirish.com/2010/the-protocol-relative-url/