When comparing CheckiO vs SoloLearn, the Slant community recommends SoloLearn for most people. In the question“What are the best resources to learn Python?” SoloLearn is ranked 9th while CheckiO is ranked 18th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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.
Pro Completely free
Pro Offline learning mode for mobile apps
Allows learning while disconnected from the net.
Pro Easy for beginners
Anyone can get started with this.
Pro Share and modify others' projects
Pro Browser-based code playgrounds
No software installation needed, just a modern web browser. On mobile devices though the mobile apps are highly recommended.
Pro Excellent mobile apps available
Pro Gamification
XP, levels, badges, certificates, etc.
Cons
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.
Con Only the most commonly used languages are covered.
C++, Java, JavaScript, C#, Python, SQL, PHP, Swift, Ruby, JQuery, HTML, CSS. You won't find anything less common like Haskell, Erlang, Elixir, Common Lisp, Scheme, Clojure, Rust, etc.
Con Limited usefulness for intermediate or experienced programmers
No advanced coding challenges. Look for those on other sites like hackerrank.