Many home wifi networks can be easily hacked into by the wrong people with the right software and that’s to say nothing of wi-fi hotspots at airports, hotels, coffee shops, etc. Criminals are always looking for a way in with so-called ‘evil twin’ software leading to a total breach of people’s personal information and passwords.
VPN’s use a secured encrypted connection, so that even if your Internet connection is intercepted it’s pretty much useless to the person who captured it. Keep in mind though that even when browsing through a VPN connection, still use https whenever possible, because otherwise the outgoing connection from the VPN server to the website or final destination you’re connecting to will be unencrypted and still subject to “man-in-the-middle” attacks.
OpenVPN is generally considered the most secure protocol for VPN’s, followed by others such as PPTP and L2TP (although some people debate that). Just be aware that not all VPN services offer OpenVPN. If you’re mostly using a mobile device, OpenVPN isn’t really an option anyway at the moment.
Another important thing for the more security conscious, is the encryption method used on the VPN server, such as AES, Blowfish, Twofish, etc…and bit level of each.
All that being said though, virtually any VPN will be much more secure than a “naked” connection.
The following are what seem to be some of the best VPN’s for security based on offering OpenVPN, encryption methods, and have a generally more security conscious vibe about the way their policies are written and services are set up: