When comparing MonoGame vs NeoAxis Engine, the Slant community recommends MonoGame for most people. In the question“What are the best 3D game engines?” MonoGame is ranked 18th while NeoAxis Engine is ranked 32nd. The most important reason people chose MonoGame is:
Support for iOS, Android, Mac OS X, Linux, Windows (both OpenGL and DirectX), Windows 8 Store, Windows Phone 8, PlayStation Mobile, PlayStation 4, Xbox One, Nintendo Switch, and the OUYA console with even more platforms on the way.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Cross-platform
Support for iOS, Android, Mac OS X, Linux, Windows (both OpenGL and DirectX), Windows 8 Store, Windows Phone 8, PlayStation Mobile, PlayStation 4, Xbox One, Nintendo Switch, and the OUYA console with even more platforms on the way.
Pro Open source
All the code is available to you ensuring you'll have the ability to make changes when you need to or even port to whole new platforms.
Pro Well-known and documented API
The framework implements the XNA 4 API, so games made in XNA can be ported to other platforms using this. This was the same API used by the Xbox Live Indie Games platform so there's lots of documentation online for it.
Pro Managed code
By leveraging C# and other .NET languages on Microsoft and Mono platforms you can write modern, fast, and reliable game code.
Pro Good community
The community MonoGame has to offer is helpful and mature.
Pro Performance on desktop
The performance on desktop platforms matches that of C++, but you still get all the pleasant features that C# has to offer.
Pro Royalty free
You can use the engine for any commercial products and keep all the profits since NeoAxis does not ask for any royalties.
Pro Completely free

Pro Simple interface
You can learn how to use Neoaxis in a few days.

Pro Excellent visual tools, map editor and resource editor
You can easily create maps/scenes and add custom objects with physics and animations in a few minutes.
Pro Lot of maps and game-modes already built-in
Has about 30 built-in maps with different game modes which can be opened by the map editor and their source code can be edited.
Pro Good IDE support
Supports Visual Studio, SharpDevelop or MonoDevelop.
Cons
Con Slow rate of updates
Versions 3.9 is overdue by a year, and version 4.0 is set to release in 2040.
Con Non-Windows tools are a bit funky
Monogame support for Xamarin Studio or Monodevelop is a bit shaky especially for library references. Only good non-Windows IDE compatible with MonoGame is Rider and that costs money & isn't open-source.
Con The developers do not actively communicate with the community
Not only have the developers driven the community away, they have actively closed the forum.
News articles have not had any changes since 2016, and the last news article still has links to the now removed forum.

Con Windows-only
NeoAxis Engine is Windows-only.
Con No community
As of 2016, the creator has completely destroyed his own community in order to silence any criticism from developers.
Con Lack of tutorials
Unfortunately, the wiki doesn't contain many programming tutorials, and the source code itself isn't very self-documented. Creating new gamemodes or AI will require lot of research for beginners.
