Asking a question such as this seems a little strange. Not very technical and a matter of choice surely?
It certainly isn’t very technical and is a matter of choice. Metal aquarium stands were used a lot more in yesteryear, nowadays it is mainly wooden types, usually in cabinet form. Having a wooden one usually fits in better with the home décor, as the finish is available in all sorts, from matt black to light pine. If it is the man of the house who is the aquarist then this will please the lady.
The metal aquarium stand is more of a bare bones affair, comprised of a horizontal base construction for the aquarium to sit on and four or more legs, with additional horizontal braces at the bottom. I assume they can be obtained in silver, black or other colours, in matt or gloss finish. They are strong, but there are dangers and disadvantages in their use.
The danger is in support. If a wooden cabinet is used, the available horizontal support from the floor is normally the full length of the cabinet and the full depth as well. Though the wooden cabinet should be checked for and have full support horizontally, it is more forgiving than metal legs as it will span small irregularities. The metal legs exert a direct pressure on one small area of the floor for each leg. An aquarium full of water and rock/sand is very heavy, therefore this pressure is considerable. If the floor is made of soft wood, such as pine, the pressure could cause a leg or legs to sink a little. Or, if the floor is uneven, one leg or legs may not have full support. Therefore it is important to check that all legs are adequately supported. I have known aquarists in earlier years place a square of metal on the floor for each leg to rest on, thus giving resistance to sinking. Any leg that is still not fully supported needs to be padded out with a suitable material so that it is. Even if the area that the aquarium is in direct contact with has adequate padding (which it should have), this will not compensate for inadequate base support.
Another consideration is that saltwater can corrode metal. As the stand is obviously below the aquarium, pollution from this will not gain access to the aquarium. The metal base is usually well painted and will resist the inevitable drips and water spills, but corrosion could eventually occur.
Usually a metal stand means that a very useful area is missing for the aquarist, and that is the under-tank cabinet. What a useful place this is for storing things such as test kits, food, a notebook and the like. Also a sump can usually be housed in this cabinet, meaning it is out of sight and no thought needs to be given to its decorative value, only to its effectiveness as a filter etc.
So metal aquarium stands are fine, with care. I bet that the vast majority of aquarists go for the wooden variety though. I always have.