Well, Doom 3 currently has the best graphics of any game and its in OpenGL....which pretty much all of Carmacks engines have been done in. Unreal Engine 3 is going to be in DX9-SM3 and its going to look AMAZING! I have to say i like DX9 and OpenGL about equal.
Because there are some graphics cards that work faster on one, and slower on the other. For instance an ATi RADEON 9500 is the undesputed KING of OpenGL, while i'ts pretty decent (But not as good as) with DX.
I was curios because somone chose "other" in the poll. lol