When comparing uScript + Unity3D vs GameMaker Studio 2, the Slant community recommends GameMaker Studio 2 for most people. In the question“What are the best 2D game engines?” GameMaker Studio 2 is ranked 67th while uScript + Unity3D is ranked 97th.
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 Quick prototyping
Pro Good user interface
Pro Well-optimized engine
Pro Has a trial version (but limited functions, can't export)
Pro Many unofficial tutorials
Most GMS1 tutorials are fine for GMS2
Pro Highly customizable IDE
Although users must work within the IDE and editor, GMS2 has many options to customize the look and feel
Pro Good documentation
Pro Huge, generous community
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 Not the best scripting language out there
GML is just weird; if you want to learn programming, it is not the best because it teaches bad habits and has many odd shortcuts and shortcomings that won't transfer to a real language
Con HTML5 export is buggy, doesn't "just work"
Con Quite expensive
Windows ($100) + HTML5 ($140) + Mobile ($400) + UWP ($400) is $1,050, plus $800 anually for each console export separately. But doesn't do anything any of the free engines can't do, and the stability and tech support aren't great.
Con Unstable
Users frequently report crashes and hangs, particularly when working with assets, and the software uses a complicated underlying meta-file structure that may become corrupted and cannot be rebuilt
Con Limited support for OOP
Con Small development team
The core programming team is only 5-10 people, with about 30 employees total, so bug fixes can take a long time to be addressed, and there aren't many official tutorials
