When comparing Codea vs uScript + Unity3D, the Slant community recommends uScript + Unity3D for most people. In the question“What are the best 2D game engines?” uScript + Unity3D is ranked 97th while Codea is ranked 107th. The most important reason people chose uScript + Unity3D is:
uScript's nodes are a visual representation of actual code blocks, and it takes advantage of C#'s reflection capabilities to automatically create nodes for any scripts it finds in your project, regardless of the source. This makes it inherently compatible with pretty much everything. Custom nodes can also be created by hand, for cases where the automatically created ones contain more elements than they actually need.
Specs
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Pros
Pro Helpful code editor
Errors show up live, as you type. Smarter autocompletion picks up your local and global variables, including nested types. Everything else is just plain smarter, from indentation to highlighting.
Pro Ships with music and sound packs
Codea ships with three great music and sound packs, composed just for Codea and free for you to use in whatever you create.
Pro You can code on an iPad and easily distribute the game
Pro Location library
Location library lets you make use of the GPS inside your iPad. Get your latitude, longitude, altitude and more with a dead-simple API designed specifically for Codea.
Pro Automatically generates nodes for third-party script assets
uScript's nodes are a visual representation of actual code blocks, and it takes advantage of C#'s reflection capabilities to automatically create nodes for any scripts it finds in your project, regardless of the source. This makes it inherently compatible with pretty much everything.
Custom nodes can also be created by hand, for cases where the automatically created ones contain more elements than they actually need.
Pro Versatile flow diagram script model
Modeled after UDK's Kismet (the predecessor to UE4's Blueprint), uScript's scripts resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.
Pro Generates C# source code
Nodes are translated directly to C# files in your project. This is great for learning to code, and also for advanced users who can use uScript for fast prototyping and then further optimize the scripts if necessary.
Cons
Con Not that easy to use
It's a lot more complicated compared to something like Playmaker. Same tasks take a lot more time.