I also prefer the middle one but there are (in all of them) very distinct patterns and hard straight lines that I don't believe you could find in nature. I would recommend that you mix this with something else (some procedural noise, perhaps, or another bitmap) to remove those things.

As for market, I don't know. There are sooooo many free sources of texture maps of all kinds in the internet that, IMO, if you want to sell yours, you have to make something that really stands out from the "crowd".