When comparing Pixi.js vs PlayMaker + Unity3D, the Slant community recommends Pixi.js for most people. In the question“What are the best 2D game engines?” Pixi.js is ranked 56th while PlayMaker + Unity3D is ranked 77th. The most important reason people chose Pixi.js is:
Pixi is a WebGL renderer, but can fall back to canvas if WebGL is not supported or turned off.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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 Easy to use
You'll need to put more time in learning Unity + Playmaker compared to something like GameSalad. But once get the hang of it and familiarize yourself with what it's possible to build with them, it's quite easy to use.
Pro Provides access to a huge list of assets through Asset Store
For those developers who can't afford an artist, or aren't skilled enough to create their own art, Unity features an Asset Store full of a wide variety of free and paid assets that can be easily added to your game. The Asset Store has more than just music and art. It also has code and modules that can be added to your game such as unique lighting or GUI systems.
Pro Third party plugins support
A lot of third party plugins have support for Playmaker. Playmaker team also invest time to add support for a lot of third party plugins.

Pro Elegant state-based visual scripting
Instead of a single "if this then that" event list which can become very cluttered beyond the most basic behaviors, PlayMaker gives each object a list of states where only certain events are triggered, and performing an action also changes state.
This allows for a clean, simple visual representation which helps break complex logical structures into smaller pieces, making them easier to understand.

Pro Powerful
It basically can do same things as scripting in Unity.
Cons
Con Not a complete solution
Pixi only provides the renderer.
Con Comparatively high learning curve
Although C#, JavaScript, and Boo have extensive documentation available online, it could still be difficult to wrap your head around the library and Unity's component based system.
Con Limited tutorials
There are not a lot videos with Playmaker tutorials. Official text tutorials are also quite limited. Even not every action has a description on an official wiki.
Con Performance could be better for 2D
Performance can be a real issue with 2D games. Unity 3D is actually a 3D game engine, and drags a lot of overhead with it.
For mobile, one could never achieve the performance of more specialized 2D engines with Unity3D.
