Black pipe is inexpensive, but difficult for some to cut/thread and some will worry abot corrosion...
Copper is expensive and typically VERY easy to cut/solder/route... Won't corrode and conducts heat well.
Plastic is really easy to route/cut, but most of the kits I've seen come with poor quality pres-to-lok connectors which is easily enough solved by using better quality pres-to-lok fittings or compression fittings.
My shop is plumbed with PEX and nylon hose. Other than leaking NPT fittings, once I replaced all of the cheapie pres-to-loks, it's been fine-admittedly, once in awhile, those with pres-to-lok fittings might leak, in which case, I lop a coupla inches off and start over. It's been about ten years now like this.
someday, I might upgrade to 3/4" nylon of maybe even copper of iron, but for now, it serves me pretty well as I have a fairly large shop with many drops/reels. To put it into perspective, it is frequently easier for me to find an airline than an outlet for an extension cord.