I've used copper on several installations, works great. Since it's malleable it will dent but not break.

Plastic is banned in many areas, particularly where it's subject to UV deterioration. It's also more sensitive to vibration stress I'm told. If it blows, it sends out a shower of sharp shards.

Just saw a very nice product at SEMA. It's a vinyl coated aluminum pipe with twist seal connectors, elbos, etc. Pricey, but nice if you think you're going to move from time to time. You can easily assemble and disassemble with the twist of the wrist, and make changes without much modification. It is being marketed in the US by Kaeser Air compressors.