For general use, OpenVPN.
For site-to-site IPsec
Idk enough about about any of the other technologies to recommend them. Wiregaurd is supposed to be the hotness that's supposed to replace OpenVPN eventually because it has better throughput and performance.
The only thing I know about it is pfsense removed it from standard deployment due to something being wrong with how it interfaced with pfsense and causing a security concern for the netgate developers.
@nerdtronics @10leej
That's not a denouncement of wireguard, that's just all I know about it.