I would say ES6 for anything that will be worked on by more than 2 people. CoffeeScript for one man show projects. But honestly...ES6 will be the norm and you

I would say ES6 for anything that will be worked on by more than 2 people. CoffeeScript for one man show projects. But honestly...ES6 will be the norm and you should know it anyway. So the question is..If you already know CoffeeScript should you keep using it ? The answer is YES ! If that makes you happy why not. But keep an eye on ES6 and learn it. More delicate question would be. If i start with JS should i learn ES6 or CoffeeScript first ?