normal map format

Actually it is not about OpenGl vs DirectX but about how each software implemented their normal map green channel coordinates - Y+ vs Y-. Two software running on DirectX can have different implementations.

So, what is more common, Maya or Max, Unreal or Unity? You can include both, or just one and leave a note for less experienced users like - normal map generated as -Y (DirectX), +Y (OpenGL) or something like this. Most software have a button for "invert green channel" anyway so it does not matter much what you are going to include.

Maya, Blender, Unity, Marmoset Y+
3Ds Max, Unreal, CryEngine Y-

Thank you.