As you can tell, Tom doesn't like plastic supply pipes! If I were going to chose between them, I'd go with pex. Copper is still the gold standard. To do it in pex, you'd want to 'upsize' the supply lines or at least carefully match the load with the supply since the ID is thinner than copper. A repipe is a lot easier with pex. On new, I'd have to think about it...lots of things to consider.