OpenVPN is one of those great open source success stories. It is used in many organisations and almost single handedly powers the whole VPN market segment. OpenVPN 2.4.0 was independently audited for security vulnerabilities twice. There are mature clients for almost any operating system making it an appealing choice as either remote access server or for extending private networks.
Using a minimal configuration OpenVPN will select a sensible set of defaults that will work well in many scenarios.