One thing to note (if you care), is that the Electron officially does not support Windows Vista. Vista's market share is about halfway between OSX 10.9 and 10.10 (both of which are fully supported by Electron). Vista is also still supported by Microsoft until 2017.
NW.js works fine in Vista, as well as OSX 10.9+. NW.js works on Ubuntu, Debian, Zorin, Manjaro, Arch, and most other Debian based Linux OS's. Electron has refused PR's to fix Ubuntu specific bugs on their platform which is concerning.
NW.js works in XP too. Currently 18% of the market is still on XP. So if you're desktop application is more general purpose or wants to have access to the late adopters still on XP, you're probably better off with NW.js (0.14.7) as Electron only supports Win 7 and up.
If you use NW.js 0.12.3 you can also support OSX 10.6+ and very old versions of Debian based Linux OS's like Ubuntu, and Win XP+. It is recommended that you do special builds just for those legacy systems though and use the newer versions of NW.js for newer OS's.