When comparing Codepen vs Glitch, the Slant community recommends Glitch for most people. In the question“What are the best cloud IDEs?” Glitch is ranked 14th while Codepen is ranked 17th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Easily export your pen
CodePen makes it really easy to export code as a zip or Github Gist.
Pro Real time output
Pro Lots of support for frameworks and preprocessors
CodePen has an impressive amount of support for preprocessors (such as Jade, Haml, Slim, Sass, Less, Stylus, Coffeescript and PostCSS). There is also plenty of frameworks and libraries to pick from (Foundation, Bootstrap, Angular, D3, Backbone, Ember etc.).
Pro Great display/profile page
The codepen profile page allows you to display all of your public pens, and control which order you want them to be viewed in. This is great for showing off your work to possible employers, other devs etc..
Pro Easily fork pens
To fork a pen only requires clicking one button, and you'll be able to modify the pen on your own account.
Pro Great community pens
You can search through other pens, either by keyword or popular, picked or recent.
Pro Unlimited number of public and private projects for free
Pro Runs a server out of the box
Perfect for building web applications, be it client-only, server-only, or full stack.
Pro Private data are kept secret, even in public projects
Non-collaborators can't access private data (e.g. API keys) which are stored in a special file, and they are deleted when a project is forked.
Pro Persistent storage
Pro Multiple languages supported
Although the only official language/framework is Node.js, you can access the terminal and install other languages via apt-get (as long as it doesn't exceed the storage limit).
Pro VS Code integration
If you feel the built-in web editor is not sufficient, you can switch to VS Code and get the full power of its plugins. You still work with the files and server in the cloud, no extra setup required.
Pro It has a friendly welcoming community of builders
Cons
Con No private pens with free account
There is an option on Codepen for private pens, however it requires upgrading to a Pro account ($9/month).