When comparing Crafty.js vs Nez, the Slant community recommends Crafty.js for most people. In the question“What are the best 2D game engines?” Crafty.js is ranked 34th while Nez is ranked 84th.
Ranked in these QuestionsQuestion Ranking
Easy to learn, based on Entities and Components, the later being class-like objects that entities inherit.
Has open function binding systems, allowing easy creation of custom components.
Pro Active community
The community is very active, so if you ask for help you'll get it relatively quickly.
Pro Open source
Completely free, no need to pay for licenses.
Pro Cross-platform development thanks to the use of mono and xamarin
Nez is built on top of monoGame and can be used the make games for many platforms (Windows, Linux, Mac, Android or IOS).
Con No IDE
If you like having some huge GUI akin to Gamemaker, Unreal, Unity, etc, Crafty is not for you.
Con Just a framework
Meaning there's no visual scene designer so you'll have to write your own.