ESLint is extremely configurable and thus has a vibrant plugin ecosystem so I think that's why it has picked up a lot of hype.

eslint also has auto-fix support to some extent. I don't know how far JSCS pushes it though.

The biggest thing is that whenever something new pops up, you can get an eslint plugin to lint it (eg: it took a wh ile for jshint to be able to take JSX or even just ES6 syntax, while ESLint got plugins for it pretty quick).

I think (don't quote me) that eslint is starting to have pretty cool Flow hooks, too.

ESLint catches more errors.

eslint is great. Through plugins it supports ES6, jsx, etc. Also, automatic code fixing.