I have seen many galvanized air systems in the years I worked with them and I never once saw a problem with the galvanized plating flaking off, I suppose it's true but an air system normally has so much junk in it that it must be filtered anyway so any small amount of flaking would be insignificant. Also black iron is commonly said to be a bad choice, about as often as galvanized, because it is supposed to rust inside but again the air must be filtered anyway so it just don't seem to be a problem, besides the pipes I have seen (both galvanized and black) are usually coated with an oily residue inside after being used for a while and rust does not seem to be a problem with either. The fact is while both types of pipe get bad raps from differing opinions either works just fine, some of the systems I have repaired/replaced were many years old and the only time I have ever seen rust to a problem is if a system has been left unused for years. I would think in the case of piping being left unused for a long time (years) galvanized would probably have an advantage but honestly either works just fine.
Personally unless cost is prohibitive my choice is Copper, especially when short runs of piping are used from the compressor to the hose outlet.