When comparing uScript + Unity3D vs GameFlow + Unity, the Slant community recommends uScript + Unity3D for most people. In the question“What are the best game engines for beginners and non-programmers?” uScript + Unity3D is ranked 25th while GameFlow + Unity is ranked 26th. 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
Ranked in these QuestionsQuestion Ranking
Pros

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.
Pro Adds an abstraction layer that helps create the game logic
It is almost like talking with Unity naturally. Actions in Unity can be coded using regular English more-so than with other game engines, which makes it much easier for beginners.
Pro None of boxes and arrows, perfectly integrated into the workflow of Unity
Almost all visual scripting solutions for Unity are based on nodes, boxes and arrows, GameFlow changes this way of working incorporating actions blocks and actions using drag and drop.
Pro Excellent product
The developer supports the users quickly and with detailed responses. He is knowledgeable on the Unity API as well as developing videogames.
Pro Integrated in the Unity inspector
No windows apart, work with GameFlow from the own Unity inspector
Pro Can achieve in minutes what would take hours with classical scripting
Due to its innovative block system and without follow tutorials or look documentation will be able to create actions within five minutes in Unity.
Pro An effective advanced prototyping and scripting tool
GameFlow allows to complete a videogame in half an hour.
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.
Con The documentation is not very extensive
The documentation for GameFlow could use some work. It's not very extensive and it hardly covers everything needed to know to build a game.
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.
