When comparing Ren'Py vs Pixi.js, the Slant community recommends Ren'Py for most people. In the question“What are the best 2D game engines?” Ren'Py is ranked 39th while Pixi.js is ranked 56th. The most important reason people chose Ren'Py is:
Available on Windows, Linux, OSX, iOS and Android.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Cross-platform
Available on Windows, Linux, OSX, iOS and Android.
Pro Active and friendly community
Pro Reasonably good at creating puzzle and point-and-click games
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.
Cons
Con Not for every genre
While technically capable of creating 2D games in any genre, Ren'Py excels in creating visual novels and has a reasonable feature set for creating puzzle and point-and-click games. Other genres are best tackled by other engines.
Con Outdated Documentation and official built-in tutorials
Unfortunately, you will have to hunt relevant info on how Ren'py script works. The Ren'Py dev has the working tutorials on his Patreon, other than that you might as well just code in Python.
Con Requires knowledge of Python to use
Con Not a complete solution
Pixi only provides the renderer.