The Best 2d Android Game Engines out there

Commercial C++ frameworks:

• unity3D: very good (available on Android, iOS, Web, Windows, OS X) [Game: Rocket Bunnies]
• Unreal Engine (commercial): the best engine but not for beginners [Game: Dungeon Defenders]

Open Source C++ frameworks:

• Ogre3D: the best open source 3d engine but it is a large framework
• Irrlicht: good performance, light framework [Game: Moblox]
• Linderdaum Engine: open source for Windows and Android
• Cocos2d-x: open source cross platform

Java Open Source Frameworks:

• AndEngine (Open Source): good performance. For documentation, look examples and read source code; but it is the Free library to begin a game project [Game: Drop Block]
• cocos2d for Android: Garbage Collector problem
• SDL is not a good idea because it is designed for framebuffer access.
• rokon: good performance and designed for mobile but project seems dead.

Physics Engine:

• box2d (OpenSource): fast and easy
• jbox2d (OpenSource): so slow on Java that I made a JNI wrapper with SWIG to use native box2d (AndEngine does the same)
• chipmunk (OpenSource): fast but I prefer box2d
• bullet (OpenSource): excellent 3D engine

Warning, with Froyo and JIT, Java libraries perform much better. But the Garbage Collector problems are always valid. With Gingerbread, the garbage collector is continous so no problem.