Here are my personal options for 2d games, based on my personal background(I developed Flash games):
- Construct2 is you want to create simple games without writing code. Simple to do standard games, hard if you need more control or more complex data structures. It contains exporters for different platform including mobiles(using html5 wrapper to execute html code, based on phonegap or something similar).
- GameMaker - quite similar to Construct2, a bit more powerful and it requires to write more code than Construct2, unfortunately in their own language. You can export games for different platforms(unlike Construct2 it generates and compile the code for each platform in native code) and for html. Each exporter should be brought so it makes this option the most expensive.
- CreateJS - the Adobe Html5 alternative. It recreates the class hierarchy from action3 flash, in html5 js. A tentative to recreate Flash in Html5, good enough. It has the advantage that it can export Flash graphics including vector graphics in an html library which can be used imported in your project.
- Phaser - A nice framework based/inspired/not an exact port of Flixel. It has nice features and it was written only for games so I would say generally it's better than CreateJS, in the same way Flixel was better than plain AS3. It can be combined with Pixi.js to webgl rendering.
- OpenFl - a flash inspired library written in Haxe. The advantage is that it can generate and compile the game in native code for virtually any platform that matters including HTML5. It can even import and use flash objects for graphics.
- LibGDX - write it in java, deploy it on multiple platforms, including html. It uses OpenGl for rendering, for the html export they use Google GWT to translate java code to javascript. It sounded for me as an interesting approach.
My advice is to pick one option and to go for it(the list is far away of being exhaustive). If you have java experience you can check CreateJS or OpenFl, if you want a codeless engine, Construct2 is more popular among html devs than GameMaker.
P.S. It seems Phaser can be easily used with ecma6.