This has nothing to do with how beautiful it looks. He said he has agressive water. The obvious choice would be pex. Not even a question. How anyone could think running copper through the attic would be better blow my mind.
PEX. And I'm scared to say this........EP fittings.
just my .02 . new design would frown upon running 3/4 to everything especially on hot water as this would increase the amount of time it takes for hot water to reach the fixture wasting water and energy to heat the water. why wouldn't you treat the water if it is so agrresive ? so the pex pipe will last longer then copper but what about the valves and fixtures? wouldn't they be attacked by the water?