My Opinion (only open source 3D engine):
- Irrlicht:
- light 3D engine
- clean C++ without dependencies and no STL.
- Not very well documented but there are good tutorials.
- Very small so you can customize it easily.
- No OpenGL 3.X driver, Direct X 10.X or 11.X available in the official SDK.
- Very good for mobile development;
- good community
- few extensions available
- Ogre3D:
- big 3D engine
- It uses modern C++ as STL, exceptions and RTTI
- Good documentation (There are published books).
- many renderers (OpenGL, DirectX and OpenGL ES...).
- Ogre3D have many extensions as CEGUI or Bullet integration, Tree nodes...
- but more difficult to extend Ogre3D if you want something specifics.
- big community
- many extensions
- Crystal space: old design and difficult to use. after few days, i quit this engine
- Horde3D
- small engine
- modern design
- light community
- no extensions
- blendelf
- small engine with some dependencies
- modern design with moderns effects as DOF or HDR ...
- OpenGL only
- light community
- bullet integration for physics
- you use lua to pilot this engine3D
in few words:
- for desktop game (or future commercial game): Ogre3D
- for first game: irrlicht
- for mobile developpement: irrlicht (Ogre3D is too big)
- for sexy effects: blendelf