Best way of setting background image for Game Menu Screen?

I wanted to know what is best way of setting a background image for game menu screen.

As far as my knowledge I can do following things:-

1> Creating a Plane and applying texture to it and pointing camera towards it.

2> Using Gui Texture.

But I am not sure which would be correct way in order to adjust it according to different device screen size.

I dont know which is the best way, but what I do is to use a skybox.
I hope it helps.