When comparing pygame vs FlatRedBall, the Slant community recommends pygame for most people. In the question“What are the best 2D game engines?” pygame is ranked 16th while FlatRedBall is ranked 44th. The most important reason people chose pygame is:
Pygame uses Python as its scripting language. Python is widely considered one of the easiest languages to grasp even for beginners.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Easy Python syntax
Pygame uses Python as its scripting language. Python is widely considered one of the easiest languages to grasp even for beginners.
Pro Very easy to understand
The API is very straightforward.
Pro Good canvas system
Pygame has a drawing system that allows the user to create and draw on an unlimited number of canvases.
Pro Continually improving and open source
Just check the commit frequency on github :)
https://github.com/vchelaru/FlatRedBall/commits/master
Plus Victor takes community input seriously and is known to shift around priorities based on the pressing needs of the community
Pro Very easy to use
Simplifies routine tasks such as adding entities and files to the game, or tuning parameters, via the FRB Editor called Glue
Pro Great community
Very active chat on gitter: https://gitter.im/vchelaru/FlatRedBall
Victor (the creator of the engine) is available throughout the day to answer questions and solve any problems that may arise, along with the rest of the community members who are ready to assist in any way they can.
Pro Extensive documentation
http://flatredball.com/documentation/
Very good documentation not only regarding the API details, but also lots of tutorials covering different aspects of using FRB, either on the code-side or on using any of its tools.
Cons

Con Deathly slow
Con Nonexistent community
No good forums, wiki, or other ways to reach other Pygame developers.
Con Very basic
Pretty much just a wrapper for SDL.
Con Pygame is a multimedia framework, not a game engine
Physics, AI and networking are not supported.
Con Messy documentation
The docs are messy, and some basic functions are infuriating to work out. There's even some places in the documentation where it's clearly wrong about how a method is called/what the arguments really do.
Con Outdated
Pygame uses a really old version of SDL and is missing some of the features developed for SDL2.
Con Hasn't been updated in years
Hasn't been updated in years.
Con The editor's UI looks dated
Although functional, doesn't look as flashy as Unity for example, which may put some people off.
