After considering which API I should used, OpenGL or D3D, I decided OpenGL. Here is my reason for choice for OpenGL:
1:M$ will copy any application and take advantage of its wide marketing sales surpassing any original products. This danger is larger if you rely on only M$ only API, since M$ can analyze application easier.
2: M$ used illegal monopoly tactics. M$ has large risk of its business. My application should not depend on API only for high risk company.