I've tried to learn coffescript at one point, but never ended up using it for larger projects. Most people I've worked with were using plain old JS.
A lot of the good parts found in coffeescript will be available in ES6. For example, there is finally going to locally scoped variables and constants. The short hand function definition with arrow will also make code cleaner. I am thinking about to switching to ES6 when there is better browser support for it.