When comparing exercism.org vs CodinGame, the Slant community recommends exercism.org for most people. In the question“What are the best coding challenge sites?” exercism.org is ranked 1st while CodinGame is ranked 2nd. The most important reason people chose exercism.org is:
Rather than merely test for code correctness, Exercism uses peer review to improve general programming techniques. Users are encouraged to comment on others' solutions, and refine their own based on feedback.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Human review and feedback
Rather than merely test for code correctness, Exercism uses peer review to improve general programming techniques. Users are encouraged to comment on others' solutions, and refine their own based on feedback.

Pro Practice with production tools
Unlike many code practice websites, Exercism requires the user to develop and test entirely offline, submitting only the finished code. This promotes familiarity with essential tools and workflow, not just the bare language.
Pro Primary focus is learning, education, and fun
Many of the other programming challenge websites focus on competition or job placement. Codingame, however, focuses on improving your skills through pure gamified education.
Pro Large community and support network
The community is a large part of Codingame's platform and the social features are well integrated into the platform. Reaching out for help, when and if needed, is very easy.
Pro Consistently updated with new content
There are always new challenges, mini-games, and competitions to be found on the site. It would be a challenge in-itself to find yourself without anything to do.
Cons

Con Custom commandline client
Exercism requires using a CLI utility to fetch and submit exercises. This is inconvenient compared to web-only alternatives, and poses an additional barrier to entry for some users.
