I know this is old, but there's one thing that is a big advantage for tinc, and it's that it supports TCP P2P

If you're behind a restrictive firewall ZeroTier won't be able to punch through it, and will fall back to forwarding packets (encrypted) through ZeroTier servers, Even if a connection could've been made over TCP to the other client (because his firewall supports UPnP or is port forwarded) which creates a tunnel directly between them.

Note that UDP connections are always better for encapsulating TCP, but P2P TCP is better then TCP through an external server with limited bandwidth.

I'm a ZeroTier user though, and i've only encountered this to be a problem once. It's nice to know it'll always work well though.

Configuration & ease of use: ZT > Tinc Connectivity: Tinc > ZT

I know ZeroTier people are looking into solving this, so this might soon be obsolete information :)

Also tinfoilhats might prefer Tinc considering there's no central service anywhere.