When comparing Cocos2d-x and Cocos Creator vs Stencyl, the Slant community recommends Stencyl for most people. In the question“What are the best 2D game engines?” Stencyl is ranked 6th while Cocos2d-x and Cocos Creator is ranked 7th. The most important reason people chose Stencyl is:
Power users can also write code in Haxe (similar to Actionscript 3) to create their own custom classes and extend the engine.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro A proven engine for mobile development
25% of iPhone games are made using Cocos2d-x.
This means you will not be alone in development, and will have access to a large community. You'll know you are developing for an engine that works.

Pro Good documentation
Documentation includes a programming guide, API reference, video tutorials and massive reference test code project showing all functions and giving working code to the user.

Pro Supports 3D models with skeleton animation
A new feature since Cocos2d-x v3.1 is support for 3D models (in your 2D game), not only this but support for skeleton animations is included too! This awesome feature allows for impressive characters in your game along with easier, more fluid and realistic animations.
Pro Great script language support
It supports Lua and Javascript with full feature support.
Especially with Cocos2d-JS you can develop games cross web and native, and the native solution have great performance with JS Bindings, much better than hybrid solution.

Pro Highly active community for questions and support
Cocos2d-x forums are active.
Pro OpenGL hardware acceleration

Pro Future-proof
Cocos2d-x is not only open source but also supported by Chukong Technologies of China and USA.
Regularly updated and adding support for the latest technologies. 2014 has already seen the release of Version 3, a new Cocos Studio development toolkit (optional) and support for new technologies like skeleton animation systems Spine and Adobe DragonBone.
Pro Greater performance than high level APIs
Cocos2d-x is C++ based engine and it has CPU advantages for most platforms because of that. It uses polygonal mesh methods for sprite rendering for using GPU advantages. (You also use quad methods for benefit CPU).
Pro No external dependencies
Because it is based on Pyglet.
Pro One code for all platforms
On top of supporting pretty much all existing platforms (except consoles), Cocos Creator (Cocos's IDE) allows you to write 1 code that runs on Android, iOS, Windows, MacOS and HTML5 (not Linux though).
Pro Easy integration of 3rd party plugins
Through the use of SDKBox you can easily integrate 3rd party SDKs and plugins for each version of Cocos2D (Lua, C++ or JavaScript), you just choose the SDKs to integrate and SDKBox will do the rest.
For example, if you want to add a rating plugin, you use sdkbox::PluginReview::init();
and if you want to add the Vundle Ad Network SDK, you use the one packaged in SDKBox SDKBOX sdkbox::PluginVungle::init();
.
Pro Allows for easy debugging
It has a built-in Python interpreter that allows for easy debugging.
Pro Very good IDE
Cocos Creator (Cocos' IDE) comes with scene editing, UI editor, animations & particle editors and whatnot. It's also easy to use and pretty intuitive if you read the official documentation & tutorials. Way way better than the old CocoStudio.
Pro Great video tutorials
Hundreds of video tutorials available.

Pro Haxe scripting available for advanced users
Power users can also write code in Haxe (similar to Actionscript 3) to create their own custom classes and extend the engine.

Pro No coding required, great drag & drop interface
Visual scripting in Stencyl is based on the MIT Scratch project, which was designed to teach programming. Script elements fit together like puzzle pieces, ensuring that data and function types cannot be mismatched.
Pro Cross-Platform
Publish iOS, Android, Flash, Windows and Mac games without code.
Pro It's a NO-CODE Program, you can add logic without code
Pro The original concept for Ghost Song was created using Stencyl
The original concept for Ghost Song was created using Stencyl 3.x
Pro Great performance on every platform
Stencyl exports your games to native code so they have great performance on every platform.
Cons
Con Poor support and non-existent community
Up until 2013, this was one of the best engines around. However, since then it was bought by a Chinese company and began stagnating - it's virtually in a slow death. Most developers abandoned Cocos in favor of more modern solutions leaving the community weak and the forums with little or no traffic. Although the Cocos2d-x Forum seems to have a decent community going.
Con No Graphics user interface
Con Modest functionality
Almost all free alternatives are more convenient, faster, and more functional.
Con Not a powerful engine
Should be used for basic games only.

Con Only available via subscription
There should be an option to buy it outright, especially considering it is written by a one man team....this is not exactly an Adobe level enterprise with shareholders, so there is no excuse!
Con Slow release cycle
Con Updated
It needs much to improve for mobile games, it was left in the era of Flash games. In Android you can not even put the native keyboard, you can not access things like native camera, GPS or native text input.
Con Tile system is somewhat inflexible
