Electron seems to have more mindshare, nwjs has some nice features like the ability to open multiple windows from the same renderer thread. In Electron, each window you open has its own renderer thread with no JS state shared between windows.

Long time ago, I used nw.js (back then, node-webkit) but too long ago to remember. However, there is bunch of posts about the subject, here is one of them: http://tangiblejs.com/posts/nw-js-and-electron-compared-2016...