When comparing Microsoft XNA Game Studio vs FlatRedBall, the Slant community recommends FlatRedBall for most people. In the question“What are the best 2D game engines?” FlatRedBall is ranked 44th while Microsoft XNA Game Studio is ranked 80th. The most important reason people chose FlatRedBall is:
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
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Easy assets
it is very easy to import your own 2 dimensional assets

Pro Very easy to use
relies largely on drag and drop elements and has been used to create notable high quality 2d games such as DLC Quest
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 It's dead
It is not getting updated and Microsoft does not recommend using it anymore.

Con Limited platform support
Only supports Xbox 360, Windows and Windows Phone
Con The editor's UI looks dated
Although functional, doesn't look as flashy as Unity for example, which may put some people off.
