Which is a best practice for setting up NTP?

A best practice is to configure the main router in your network to a known good trusted time source by its DNS address. All devices in your network should then be configured to point to this trusted router. All time sources should pyramid out from the central source of time in your network. Configuring all devices to a public NTP server is not a best practice because multiple firewall entries will need to be configured. Configuring all devices to different NTP servers for redundancy is not a best practice because all devices should synchronize to the same master. Configuring all devices as master servers is not a best practice; only one master should exist.