OpenGL or Direct3D?

I've been thinking of making some sort of 2d game with little 3d maybe, but I'm not sure which is better/easier to learn: OpenGL or Direct3D. Can someone clarify me what are their strong/weak points, or which is generally simpler or easier to learn, cause I'm not going to do anything big.

You might wanna try SDL; it's a library that provides more high level functions and uses OpenGL as a backend for the graphics; it also does sound and input and shit, which OpenGL by itself doesn't.