Tailscale is an automatic no for me. I won’t use proprietary software for something as important as this. Even with tincs history I’d much rather go with opensource.
If you haven't seen it, an open source implementation of the server: https://github.com/juanfont/headscale.
The Linux & Android clients are fully open source. The Mac GUI is closed, but the "Linux" client runs on macOS, sans GUI. (Also runs on BSDs, and I believe Windows)
At that point, only the iOS and Windows GUI app is closed, but they're both super thin wrappers around the open source Go implementations.
But, yes, it's true that we're not entirely open. We'd planned to release a simple server implementation when we got it cleaned up, but then Headscale beat us. That seems like the most important missing bit.
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...