Whether OpenGL or D3D is "better" depends on what''s important to you. One or the other will look better depending on the category you''re looking at. In my opinion, it goes something like this:

Ease of use = OpenGL
Portability = OpenGL
Driver quality = D3D (how good the existing drivers are)
Hardware support = D3D (how many vid cards support it)
Rate of development = D3D
(Development of OpenGL itself is very slow compared to the changes and additions being made to each version of D3D)
Learning curve = OpenGL (MUCH easier to learn)