WireGuard is like a modernized version of the SPTPS protocol --- SPTPS is a denatured variant of TLS --- that tinc uses, (ordinarily) coupled to the Linux networking stack. It is something you would build a modern version of tinc on top of, not a competitor to tinc. See Tailscale for an example of something that looks a lot like tinc, but built on WireGuard.

Tinc's security track record has not been especially great†, and while WireGuard and tinc are both written in C, tinc is a great ghastly blob of C, and WireGuard was written defensively by a vulnerability researcher to minimize attack surface --- the whole thing is about 4000 lines of code, and can be run without memory allocation.

So if you were just comparing SPTPS to WireGuard, it'd be no contest at all: you'd always, always prefer WireGuard. And that's what most people should do, because most people run simple access VPNs that don't need elaborate mesh routing features. For the minority that do, for now, there's Tailscale and Tinc; maybe Tinc can do a 2.0 on top of WireGuard, with its userland components in a memory-safe language.

† This, in particular, is not the commit message you want to see in a fix for an error oracle vulnerability: https://www.tinc-vpn.org/git/browse?p=tinc;a=commit;h=d3297f...