Which of these do you use on your relays?
Some people may or may not consider relays (in general, overlay network nodes) to be a separate class of unix box subject to whatever various concerns, differential administration, etc.
Let's call it a unix box. It's FreeBSD 11.
If you use FreeBSD's packages, ntpsec... while having forked the former ntp.org client in a fine direction (see ntpsec's website)... is not yet available in pkg form, the rest are. It compiles and works fine. Among the rest, if you want to interface with GPS, PPS, radio, old random HW, use exotic timing schemes, graph logs, kitchen sink... that's more like ntp.org, which has a historically large community, and is still the one shipped with the FreeBSD base system. OpenNTPD is very lean and from the security family of OpenBSD. In the bump style of ntpdate, tlsdate is more of a comparator / last ditch anti-censorship tool.
For basic network sync, try openntpd. New to FreeBSD and want their help, go with their base ntp.org. Old school time-nut, ntp.org, or if... Looking for other new perspectives, ntpsec. Stuck in a hole and can't tell noon from midnight, tlsdate.
There's no single answer. I've used them all.