Thanks to the increasing popularity of Babylon, it has a growing community of helpful developers. It's easy to find help on their [forum](http://www.html5gamedevs.com/forum/16-babylonjs/).
Ranked in these QuestionsQuestion Ranking
Pro Supports WebGL w/ canvas fallback
Pixi is a WebGL renderer, but can fall back to canvas if WebGL is not supported or turned off.
Pro Will be familiar to ActionScript developers
Pixi.js uses a code structure that's very similar to ActionScript.
Pro Small (but helpful) community
Thanks to the increasing popularity of Babylon, it has a growing community of helpful developers. It's easy to find help on their forum.
Pro A good amount of easy to understand resources to learn from
Babylon provides a playground where you can explore examples and play with the code.
The official documentation offers a wide variety of well-written tutorials on topics from beginner to advanced.
Additionally, there are many tutorials written by the community available that you can find by doing a google search.
Pro Great base shader material
Pro Actively developed
Babylon has great project health, with activity on Github daily for bug fixes and new features.
Con Not a complete solution
Pixi only provides the renderer.
Con Young project
Babylon is quite young compared to many of it's competitors (released in 2013). The community is still somewhat small, however growing quickly.