Originally Posted by
since
You're a little confused.
All libraries are going to be based on OpenGL or DirectX (or I guess in special situations directly interfacing with the gpu/driver or something aside the point).
... anything we will ever be using for general graphics will be OpenGL or DirectX. All of those libraries you find are built on top of OpenGL or DirectX, they're just designed to make using OpenGL or DirectX easier.
Using OpenGL directly for example you need to be a lot* more aware GL states, texture calls, etc etc, where as those libraries you just give some simpler parameters and they do that work for you.
What's better? Better question, how determined are you, what is your goal, what is your experience level?
If it's all for the lulz to play around on start with SDL or Processing. (Processing.org)
If your more serious OpenGL/DirectX and Shader languages like GLSL/HLSL.
OpenGL is not just for 3d graphics. OpenGL is the industry standard graphics API, DirectX is a dedicated API implemented for use on Windows systems specifically.