I've never used anything but PVC. I'm well aware of all the theories and warnings about exploding pipe, but it's never happened to me. Even if it did, I doubt it would explode -- at the first fissure, the air escapes and the danger is gone. While I've never had any break due to pressure, I have bumped a pipe and broken it -- big whoosh, then nothing.
It's definitely the cheapest, quickest and easiest solution. In fact, it's so cheap, if you get concerned about a section, just rip it out and replace it. Use sched 40, of course.
Next, would be galvanized pipe (or black iron if it's not exposed). But, as mentioned, you need a cutter, thread vise, and a threading wrench and dies. I bought a cheap rig from Harbor Freight which has served me faithfully, but we only use it occasionally. A Rigid threader can run into hundreds of dollars.
I never considered copper pipe. Too expensive in the diameters needed. Easier to work with than the iron pipe, but I don't think I'd trust getting every joint sweated properly to hold that much pressure.
Don't think about the flexible hose method -- it will droop between fasteners and collect moisture.
I run all my pipe overhead and at a slight angle away from the compressor for drainage. I have drop pipes that come down to the connections, and each drop pipe is then extended a couple of feet below the connection and terminated with a plastic ball valve. Condensation drops below the connection tee, collects in the lower pipe, and I open the ball valve periodically to drain the water.
Part of the remodeling I'm doing to prepare my commercial property for sale is to remove any potential liabilities. Since I'm taking my compressor with me, and have no idea what kind of business will buy the shop, I took down the PVC airlines. They had been up for about 11 years, and there was no sign of any degradation. Some of the drop pipes were exposed to partial Florida sunlight, and I especially checked those pipes to see if there had been any weakening from UV. What I did was to deliberately try to break the pipes. A couple snapped easier than the others (but still with difficulty), leading me to think that any PVC pipe exposed to UV should be replaced in 10 years. That's my advice to myself; don't rely on my time estimate.
I will be using PVC in the new barn.