I like copper. My steering lines are copper. I used the type with the blue plastic coating, mostly because it looks cool, and my brother in law owns a lpg company and gets it wholesale. I agree on the unknown factor of what is in the plastic, and copper is a natural biocide. BUT, pex is so easy to use, repair, add to, etc. not to mention way cheaper. And it comes in the internationally recogniced colors of hot and cold