When comparing Codecademy vs CheckiO, the Slant community recommends Codecademy for most people. In the question“What are the best resources to learn Python?” Codecademy is ranked 1st while CheckiO is ranked 18th. The most important reason people chose Codecademy is:
Right from the start, users write code. They start small in an environment that has constant feedback and gradually progress to more complex concepts. Users can see code results instantly, giving great feedback.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Interactivity
Right from the start, users write code. They start small in an environment that has constant feedback and gradually progress to more complex concepts. Users can see code results instantly, giving great feedback.
Pro Excellent progression
Codeacademy doesn't overwhelm beginners with information. It gives bite-sized information, the bare minimum needed to finish a task and get to the next one. As the course progresses, it slowly fills in background information.
Pro Good editor
Codeacademy has a powerful, beginner-friendly integrated development environment (IDE) that can also be used outside of curriculum.
Pro Bite-sized lessons
Each lesson in code-academy focuses on a single concept, and repetition is provided to drill the concept.
Pro Mostly free content & best progression series for beginners
Pro Community forums
It has forums which can be used to discuss with other learners

Pro Community backed solution reviews
Users can publish their solutions for different problems and other users can review the code and give their opinions on how they would have solved the problem.
Sometimes, some of the most active users get their code reviewed by Guido Van Rossum (the creator of the Python language) himself.
Pro Available in multiple languages
CheckiO crowdsources translations for problems. Currently problems have been translated in 10 languages. So it's highly possible that eventually more languages will be supported.

Pro Ability to create new challenges
New missions can be created and uploaded using GitHub. After that is done, it's suggested to CheckiO and if it fills all the requirements after being reviewed by a CheckiO team member, it's pulled into the game.

Pro Challenges from GitHub, O'Reilly, Dropbox and Hubspot.
Cons
Con Not the best structure for quick refreshers
The content of the lessons is aimed very much at people just starting to learn how to code. This is perfect for beginners but if you want to use Codecademy to refresh your knowledge the lessons are not designed to be quickly done.
Con Lack of context
Codecademy is great for providing a hands-on approach, but there is a lack of context regarding how to start a project in real life. While users may learn how to code using Codecademy's interface, they may not have any idea how to code independently.
Con Sticks to pretty basic
Con Deleted a lot of content
A lot of free content has been taken away, for example the PHP course was removed from the site.
Con Buggy
Codecademy is known to have many bugs which interfere with the editor, resulting in error messages despite having the correct answer.
Con Allows infinite loops to run
If you run an infinite loop, the browser freezes. Many other similar websites will give you an error, preventing the loop from running. Though not a bug, the lack of feature to stop infinite loops from running can be quite frustrating to beginners.
Con Not for absolute beginners
CheckiO does not teach syntax, instead it teaches how to solve problems using a particular programming language therefore some basic programming knowledge is required to start.
