When comparing Starling vs PlayMaker + Unity3D, the Slant community recommends PlayMaker + Unity3D for most people. In the question“What are the best 2D game engines?” PlayMaker + Unity3D is ranked 77th while Starling is ranked 78th. The most important reason people chose PlayMaker + Unity3D is:
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.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Lightweight
Starling is just 12k lines of code and doesn't try to do everything — but what it does, as efficient as possible.
Pro Feathers User Interface Components
With Feathers, you can easily add great user interfaces to your games — or even create business apps with Starling.
Pro Free and open source
Starling is available for free with code available on GitHub.
Pro Strong community support
Forum is always active with knowledgeable developers and with lot of inside info, and post mortems.
Pro Works with Flash
With UI, you can design it in Flash Professional (powerful 2D editor), export to swf file, use GAF convert swf file to gaf file, finnally, load gaf file to Starling. GAF can convert a lot of file swf to one atlas. Alway use same resource in design files (fla) to optimize atlas size, avoid duplicate asset in atlas.
You can use flash to create animation for starling.
Pro Hardware accelerated rendering
Let the GPU do the rendering, the CPU has more important tasks to do.
Pro Cross Platform
It can be exported to web flash player, iOS, Android, Windows, and OS X
Pro Works with AIR's native extensions
Using AIR's native extensions any native code that can be written can be run and used by the game engine.
Pro Constantly updated
New features are added regularly.
Pro Better performance than most alternatives
Starling can run more animated display objects than Unity2D and many others frameworks at 60 fps.
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 Poor text/font support
It supports only 4 features for text rendering:
- bitmap font with batching.
1.1. basic distance fields with support for outline and filters via MeshStyle.
1.2 the new multichannel distance field, the ultimate solution for bitmap font rendering. - Draw and upload texture in runtime
So every new text field required texture uploads or vertex/idnex buffer uploads.
skipUnchanchagedFrames keep the backbuffer static for scenes without changes between frames, leveraging a good rendering optimization.
Con Engine supported mainly by one man
Its open source but in most cases community features or pull request are canceled.
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.
