When comparing Gosu vs SFML, the Slant community recommends SFML for most people. In the question“What are the best 2D game engines?” SFML is ranked 35th while Gosu is ranked 50th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Lightweight
Gosu is not a game development framework, only a media library that happens to be suited to game development. (Kind of like SDL in the C world.) That means the interface is relatively small.
Pro Mature API, actively maintained and developed
Gosu has been under development since 2001. It is mature and has several toolkits built on top of it to provide additional functionality.

Pro Cross-platform, even mobile, using Ruby
Pro Very efficient and usable
Pro Zlib/PNG license
In short, SFML is free for any use (commercial or personal, proprietary or open-source). You can use SFML in your project without any restriction. You can even omit to mention that you use SFML -- although it would be appreciated.
Pro Can be combined with OpenGL
If you hate something about the way SFML handles graphics, you can just combine it with OpenGL. It's completely smooth and works as expected, without any additional dependencies.
Pro Active community and wiki
You can ask questions on their own personal forum which is full of users, and their wiki is constantly being maintained. They even have an IRC.
Pro Works on every platform
SFML 2.2 brought forth Android & iOS functionality, and SFML games work on Linux, Mac and Windows out of the box, since SFML is written with OpenGL.

Pro Great documentation
SFML is very well documented, even with short examples of use for many functions and modules. Furthermore, there are books like 'SFML essentials' and 'SFML for game development' which teach you how to use this library to its fullest.
Pro Good for OpenGL
If you are thinking about using OpenGL, look no further, you can open a window, and handle events in less than 15 lines, and it provides input, time, and even networking, plus alot more. It has become my favorite c++ library :D
Pro Great library
SFML is a collection of modular, well designed libraries you can implement an engine or game on top of. The API provides tons of good documentation and is very straightforward to use. You can get a game up and running with SFML quite quickly and with minimal effort.
Pro Clean code
An SFML project's code-base is usually clean and easy to read. All public SFML classes are under the namespace "sf" so it is easy to tell which code is yours and which belongs to SFML (of course you can stop this by typing using namespace sf;
).
Pro Available in many languages
There's support for many languages besides C++, current supported languages are: C, .NET, Crystal, D, Euphoria, Go, Java, Julia, Nim, OCaml, Pascal, Python, Ruby and Rust, and this list is constantly growing.
Pro Beginner-friendly
SFML is extremely beginner friendly and even provides pre-built libraries for your IDE of choice on Windows. Besides the fact that it's extremely well documented, they also have a set of tutorials that walk you through every module.
Pro Modern C++11 implementation
SFML is one of the few good C++ frameworks out there to actually make full use of the language. It's extremely well optimized and it plays well with anything you throw at it.
Cons
Con Deploying Ruby apps is a mess
Games built with the Ruby to .exe "compiler" do nothing more than extract your source code and Ruby.exe to %TEMP%, then run it. The code is not really compiled at all. The process for wrapping games as Mac apps is a bit nicer, but you'll need a paid Apple Developer subscription to code sign the app, or users will see a warning/error when running your game.
The only way to really compile Ruby is to use RubyMotion, which does not work on Windows and requires a paid subscription on top of the Apple Developer one.
(This Con is not specific to Gosu. Deploying Ruby code has never been fun.)
Con Relatively slow
Compared to SDL2, GLFW, it is slow.
Con No GUI editor or IDE
Does not include any IDE or media editor. It's purely source code.
Con May take longer to learn and understand
Con Messy sprite management
Sprites retain all of the operations applied to them, whether that be a new position or a rotation. This makes sprite management somewhat annoying.
Con Not specifically a 2D game engine
It isn't really an engine, more of a collection of modular, well designed libraries you can implement an engine or game on top of.
