When comparing CoffeeScript.org vs exercism.org, the Slant community recommends exercism.org for most people. In the question“What are the best resources to learn CoffeeScript?” exercism.org is ranked 1st while CoffeeScript.org 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 Provides an in-browser interpreter so you can practice while you learn
The site also provides an interpreter right on the page, which will let you run CoffeeScript in your browser, and show you the equivalent JavaScript as you type.
Pro Excellent resource for those already familiar with JavaScript
If you're already familiar with JavaScript, The official CoffeeScript website is an excellent resource for picking up CoffeeScript - the main page provides a quick reference for all of the language's features, complete with examples, side-by-side with their JavaScript equivalents.
Pro Provides clearly annotated source
If you're the type who likes to really dive into the details of the tools you use, the CoffeeScript website also provides clearly annotated source for the language itself, to clear up any questions you might have.

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.
Cons
Con Site design/format can be hard to follow
All the content is listed on one web page, with very little white space breaking lessons apart. It can be a bit difficult to follow.

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.
