Electron is more active than NW.js looking at their github repos, it has had 25 releases since the last NW.js release for example. Visual Studio Code choosing electron was a big external validation too in my opinion. (no idea if that was a factor though)
Interesting. I am developing a desktop app using nwjs because a) many popular apps were made using nwjs and b) I like their documentation.
It is fascinating because both of them are quite similar in nature and picking one instead of the other doesn't mean you're missing out on a major feature.
I know I had some issues building LT on Debian 7 (long time ago now) -- and the whole bundle node+nw.js appeared to be a bit fragile. Hopefully Atom Shell is a more stable/sane/better tested platform -- it appears that's what the reasoning was if I'm reading what appears to be the relevant issue correctly:
I think it was because they ran into problems with NW (esp. freezes on OSX), but I'm not entirely sure if this was the main reason for switching to Atom/Electron.