The most popular VPN protocols in use today are PPTP, L2TP/IPsec, SSTP, and OpenVPN. Each of these has its strengths and weaknesses and it can be difficult to decide which is the best choice for your situation. Not all VPN providers support all of these protocols, SSTP being the notable exception, but most will support the other three. I hope that my independent review of them, will help you to decide, which of these is the best for you.
The main facets to consider are; reliability, security, performance, and ease of use.