Preferably I like the Direc3D API because of its simpler framebuffer control system.
that is what happens with most of people. DirectX plugin works with intel gfx but OpenGL plugin no.
i use either or depending on the game im playing
The big question, it depends on your OS too.
I don't notice such a slowdown in OpenGL since i'm still using XP.
The only thing I dislike about OpenGL so far is not working with the Watchdog, but that's only for 1 or 2 non-fullspeed games and my crappy rig.
In general, OpenGL is way better.
...
This coming for a ATI user.