Which protocol provides the highest level of security for VPN's?

updating for 2020

IKEv2 is a nice mix of speed and security, but is developed by Microsoft and is partially closed-source. That means that individuals cannot check some of the code for anything that might be malicious.

OpenVPN is the standard for security and is fast, but it is bulky and bloated and can slow down older devices. OpenVPN is also completely open-source which means that anybody with experience with its programming language can check it for anything malicious at any time.

WireGuard is a newer VPN protocol that promises to be faster, more stable, and more secure than other protocols, but is still in development. There are other proprietary protocols based on it, such as NordVPN's NordLynx.

Feel free to correct me on anything I might have gotten wrong!