They are both based on WireGuard (kernel-space and user-space `wireguard-go`), so I guess there's no significant difference in performance for typical usage.

In terms of stability, Netbird has been pretty good for me. I've been using Netbird as the backhaul network for my laptop, phone and inter-site k3s cluster for several years without major issues.

One major downside of Netbird is that its Android client can be quite a battery drainer [1]. (It keeps your fingers warm during winter, though!) As for Tailscale, it offers some neat features like Funnel, which is missing in Netbird, but in my case, covered by DNS and k8s Ingress.

[1]: https://github.com/netbirdio/netbird/pull/3379

Netbird seems (or perhaps is?) newer. It didn't have some basic features baked in when I last looked into it, e.g. you couldn't switch accounts on the client https://github.com/netbirdio/netbird/issues/3273 and if I had an account associated with a single team, then that account couldn't be invited to or be associated with additional teams.