In their current states, Webpack is for the production applications, JSPM for development / little ES6 apps, and SystemJS is used for Node.js.

- Webpack supports much more than just ES6 (and more people work on it), so you probably want to use it for production apps.

- JSPM allows you to load ES6 library by transpiling them on-the-fly, which is great for simplicity.

- SystemJS works by itself in a Node environment, you don't need JSPM for it.

Guy Bedford has made a great tool with JSPM.