I would prefer to begin from grsecurity, but it is not available up to date for my budget.
I would also try HardenedBSD, but it is only amd64 now? And how many active developers there are? one or two? OpenBSD looks as the only viable option for me right now, may be one another is a systemd free distro like Devuan with a hardened kernel like by @anthrax, but I am too unskilled even to understand what are improvements of @anthrax kernel for me without a good doc for it in the existence, and on the other hand OpenBSD is famous with its very good documentation. I guess it is a huge work to harden Linux installation to a level compared to OpenBSD, there is some interesting work which is by Whonix but unfortunately with systemd, and it seems someone from that community is referring to isopenbsdsecu.re site, so it looks to me like a OpenBSD vs Whonix dispute, excuse me if I am wrong.
