This seems to come up every now and then in conversation. I use copper pipes. Almost everyone I know is switching to running PEX due to low cost and easy installation. Here is my take on the situation.
Copper pipes have been used for hundreds of years and typically have a lifespan of 50-100 working years in domestic water situations. The only thing that brings this lifespan down is acidic water, and frozen pipes. A split copper pipe can be easily repaired though, so freezing isn’t all that bad. Plus, unfreezing copper is easy – heat it with a torch! On the downside, copper is twice as expensive as PEX. Installation of copper pipe requires a basic propane torch, solder, and flux.
PEX piping is relatively new (a few decades) and has an unknown lifespan. PEX is plastic and all plastics leach some chemical into the water. If this is a safe amount or not, I’m not sure, but I feel unsafe using it in my home. PEX is cheap, flexible, and when it freezes it typically doesn’t burst (though it can). On the downside, PEX can be chewed through by mice and rats and it can’t deal with high temperatures or UV rays (no outdoor exposure). PEX requires special tools to install.
I will gladly pay more for the copper and sweat it in myself. I like the fact it doesn’t leach chemical. I like that it looks nicer when exposed (PEX is ugly). I like that it is safe around rodents (mice and rats are commonplace on the homestead at times). And I also like that I can heat it with a torch if it freezes.