First of all, this an awesome terrain, somehow it really manages to capture my attention.
I got to say that the first version is by far the best, it portrays a superb atmosphere with just the right amount of lighting/fog/clouds.
The 2nd and 3rd version kind of screw up the atmosphere because the background is too white and thus jumps out too much, these types of terrain should be gloomy, dark and monotonous. Making anything jump out too much gravely diminishes the quality of the terrain.