There has been a lot of discussion about a lunar colony or at least a base as a precursor to sending humans to Mars. The advantages cited are its proximity to Earth, the use of telerobotics for construction, and the fact that we’ve been there before. My position is that it would be far easier to establish a self sufficient colony on Mars with existing technology.
One thing everyone agrees on is that local resources will have to be used. We now know that There has been a lot of geological and hydrological activity on Mars that has segregated and concentrated useful ore bodies that can be exploited with current extractive technology. One type of mineral of interest is the occurrence of iron and magnesium carbonate formations on the surface. Magnesium carbonate is easily converted by heating to magnesium oxide, the primary component of a type of cement that I am researching as a construction material for Mars. The widespread occurrence of sulfate salts also gives reason to believe that metal sulfide ore bodies are also available there. This type of ore can easily be refined with simple electrolytic equipment. The same metal refining on the Moon would require grinding and processing basalt with a lot of heavy equipment.
I would argue that Mars also has a more friendly environment. First, it has higher gravity than the moon, at 38% of Earth’s gravity. This may prove to be significant in minimizing the health effects of reduced gravity. The higher gravity would also aid in many industrial processes such as ore separation and concrete consolidation. Mars also has an atmosphere, however thin. While 4 to 8 millibars may not sound like much, it is enough to burn up a lot of micrometeorites before they reach the surface, reducing the danger of micrometeorite damage. It may also help reduce the danger of galactic cosmic rays, but that will need to be tested. One thing that is certain from my own research is that the thin atmosphere is enough to allow magnesium oxychloride cement to cure before a significant amount of water has evaporated from it, and prevent boiling during the curing process. On the airless Moon, this type of cement would boil violently and the water would evaporate before it would cure. The total lack of atmosphere on the Moon would preclude the use of any cement that depends on water for curing.
Dust will be the biggest challenge to machinery in either place, and I argue that it is much less of a challenge on Mars. We have already studied lunar dust, and it is composed of fractured particles that retain sharp edges and points, with no mechanisms for smoothing the surfaces such as wind or water movement. This makes Moon dust very abrasive to machinery (and air seals) and very irritating to human tissues on contact. Mars has annual wind storms that blow dust around the planet, and has had flowing water recently in it’s history. This would serve to smooth out Martian dust particles to something more closely resembling the kind of material found on Earth, which we can more easily deal with. As further evidence, we have had rovers survive multiple dust storms and keep operating. I would say this is as much a testament to the Martian environment as it is to NASA engineers. Additionally, the dust has been found to be largely magnetic, meaning that magnetic filtration could be used to keep it out of habitable spaces.