When comparing NW.js (w/xvfb) vs Sciter, the Slant community recommends NW.js (w/xvfb) for most people. In the question“What are the best tools for building cross-platform desktop apps with web technologies?” NW.js (w/xvfb) is ranked 2nd while Sciter is ranked 6th. The most important reason people chose NW.js (w/xvfb) is:
The integration of Node with the DOM in NW.js opens up a number of new options in how your headless testing workflow can be facilitated. The distinct separation of JavaScript contexts, the introduction of a separate node context, and the ability to cross communicate, offers a lot of power and flexibility.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Node integration
The integration of Node with the DOM in NW.js opens up a number of new options in how your headless testing workflow can be facilitated.
The distinct separation of JavaScript contexts, the introduction of a separate node context, and the ability to cross communicate, offers a lot of power and flexibility.

Pro NaCl support/integration
Access to the Native Client offers up more options in implementing your testing workflow.
Pro Multi language
Support for C++, C#, Delphi, D, Go, Rust, Powerbuilder. See Go bindings on GitHub. The binding for C# on GitHub, SciterSharp does not seem to be free: in a commercial product you should acquire a commercial license.
Pro Lightweight
Only a single native DLL.
Cons

Con xvfb Requirement (for now)
Headless is on the NW.js roadmap, but for now xvfb is necessary to get going. The community has done the work and you can find the details here.
Con Linux version is not very mature
The Linux version is missing HTML/CSS features when compared to the Windows version.
Con Not fully HTML5 compliant
Lacking HTML5 functionality and W3C standards: grabbing a library like JQuery or Bootstrap and use it in Sciter will not work.
Con Not WYSIWYG
Not WYSIWYG like WebForms or WPF.
