Software: the client works with its own engine, without using any resources from your PC. Is an option more suitable for those who usually play with low FPS, as this option generates the maximum to increase them. However, using this option, the effects of the ambient lights are disabled.
DirectX: is one of the most famous graphics out there, and uses a little more computer resources than software. There are two options, Performance and Compatibility. The Performance option aims higher FPS, while Compatibility is recommended for those who usually have some errors while playing, which causes Tiba to close, or some alteration in the image. The lighting effects are released.
OpenGL: does not differ much in relation to FPS when compared to DIrectX. Suitable for those who have some imaging problems when using DirectX. Some users also say that with more modern video cards, Tibia runs better with OpenGL. The ambient lights are working.