If you live somewhere with hard water, replace the copper with pex. The minerals eat away the pipes. We had a home in a hard water area once, sooo many pinhole leaks over time, and water heaters had really short life spans. If your water doesn’t require a softener, then keep the copper. If there’s a chance the pipes were exposed to freezing conditions at all in the past, look for bulges in the copper which will indicate weakened lines that should be replaced.