I imagine CPVC would be the default, since it's a lot cheaper to purchase and install. There's a good article in the latest Fine Homebuilding touting PEX, but if PEX isn't an option, I'd go with CPVC. I just re-plumbed my house (changed from copper to CPVC), but our local water and soil don't play well with copper. You might check with the city to see if they have any recommendation. You may find this to be somewhat of a religious issue.