There is a fascinating book called "Salt: A World History" by Mark Kurlansky. I can't quote from it as I have lost my copy but along with fascinating historical tidbits, he relates that salt was originally sourced from all over the world by a variety of small scale production methods. The refining processes were often crude, resulting in many of the natural minerals being left in the final product, thus giving each salt a unique flavor. Refining processes were eventually developed that removed the impurities and allowed the development of uniform and consistent grain size and the ability to do so on an industrial scale. The public eventually began to expect clean salt of uniform size and began dismissing other salts as dirty and a clearly inferior product. So the recent interest in "natural" salt is more of a return to the early sourcing and production methods and a renewed acceptance of the presence of minerals in salt as a positive attribute.
All of which is to say that it is perhaps more of a personal preference for one salt or another than one being better than the other.
Of the history related to salt, the story i found most intriguing is that Mahatma Gandhi became famous for the simple act of picking up salt off a beach as an act of civil disobedience. The British colonial government of India wanted to promote the use and development of a salt mine back home rather than having the natives use local salt. Some communities of coastal Indians made a subsistence living by harvesting salt from nearby beaches. When the British passed a law prohibiting this, the effect was to deny these communities any form of economic activity, essentially dooming them to starvation. Upon hearing of this, Ghandi, then relatively unknown, proceeded to walk hundreds of miles across India for the singular purpose of defying the unjust law, letting his non-violent intentions be known. As news of this potential act of civil disobedience spread, hundreds joined him in his walk to the beach. By the time he arrived, the crowds were enormous and the world press was recording his every move. All he did was to reach down and pick up some salt.The resulting coverage was so embarrassing to the government that the law was repealed, virtually immediately, Ghandi became world famous and civil disobedience spread around the globe. A little salt really can go a long way.