Unity's modular system and usability allows for you to quickly develop a prototype of your idea. It has features like drag & drop editing, shaders, animation and other systems already in place to allow you to dive right into developing your game.
LibGDX is a low-level engine meaning it requires much more coding than other higher-level engines. Although this allows for greater customization, it can make things more difficult for beginner programmers.
Game Maker Studio uses a tiered service beginning with a free options. With this option you have basic features that can still be used to make a decent game. If you decide this engine is for you, the first paid option is only about fifty U.S. dollars. This means you wont have to commit hundreds of...
Language does not support actual objects, structs, real data types, functions, overloading, even argument naming. Developers generally have to code around the lack of these features in very tricky ways.
According to the Cocos2D-x website, 25% of iPhone games are made using Cocos2D-x (A Cocos2D mobile variant.) This means you will not be alone in development, and will have access to a large community and know you are developing for an engine that works.
The documentation contains a reasonably detailed language overview, and a somewhat-generated list of the included modules, classes, and methods. Module descriptions are rather lax, but usually present. Method descriptions tend to be short, and a majority of them contain no usage snippets; most para...
Oxygine is written in C++. It provides easy to use API, which is designed with "do more with less code" philosophy. It uses a managed scenegraph system that takes care of rendering and updates, and provides ability to extend with custom rendering and updates.