Differences among PPTP, L2TP, SSTP, IPSEC, IKEv2, and OpenVPN

L2TP generally offers better encryption and NAT penetration. If PPTP fails, try L2TP. If both fail, try IPSEC, SSTP, OpenVPN. See details here: http://www.5uf7.com/news/vpn/id/10044/