Denny, I love the question. We can discuss this for months. My answer, subject to change at any given time, is black iron pipe. I plumbed my compressor in with black iron, much like TP Tools recommends, 10 years ago. I have not had a problem. I recently decided to extend the coverage and added about 30' of both 3/4" and 1/2" black iron pipe. I have mixed galvanized fittings on occasion without concern or notice. I think copper would probably work but have some concerns about the thickness of the walls of the pipe. Rust, inside the pipes I guess is the long term question. The outside of the pipes is a non-issue. I live in the desert and for the most part we don't allow much rust. I'm betting I won't live long enough to see my pipes rust out from the inside but we'll see.
Geo
