For what? Technically you probably mean OpenGL vs Driect3D because DriectX is an all inclusive input/video/sound system where OpenGL is just a graphics library.
I dont think one or the others better. Doom 3 was OpenGL. It was considered to have the best graphics, and then HL:2, Direct3D, (arguably) took its place. Now Quake 4, OpenGL, has taken its place.
