Opera VPN works only through the Opera web browser, and it shouldn't be used for sensitive communications. Once very fast, Opera's VPN connections were painfully slow in our most recent tests. The Opera VPN mobile apps, which were full-fledged VPN services that performed decently in our 2017 tests, unfortunately closed up shop at the end of April 2018. There's one good feature, though: Opera VPN streamed Netflix successfully from all of its server locations (there are only three of them), which is more than many paid VPN services can do.
NordVPN holds the number one spot considering all of its features combined in a VPN that works at an excellent level. Regarding security, NordVPN has a proven DNS leak protection, including the IPv4, IPv6 and WebRTC address protocols, as well as mobile protocols such as IKEv2. In addition, PPTP, L2TP, IPSec and OpenVPN are also used to ensure the most secure and up-to-date protection service. Double layer encryption is employed in the tunnels which NordVPN hosts, which is nearly impossible to break, even if super computers are working non-stop for years trying to decipher it. In the event that someone sniffs some of the traffic, it will still be encrypted, so NordVPN has set the bar high for the most secure VPN requirements.
Regarding privacy, ExpressVPN is a logless type of VPN and any traffic that goes through is considered safe from prying eyes. ExpressVPN also uses a strong encryption protocol with 256-bit ciphers, so even if traffic and communication data somehow get sniffed, they will be locked with the encryption algorithm and appear as gibberish symbols rather than bare text.
Hotspot Shield depends on a custom VPN protocol that's not been publicly analyzed by independent experts. We don't know how private or secure it really is. The company has been accused of spying on users (it denies the allegations), and complaints abound online about Hotspot Shield software installing on PCs without users' permission. All this, and the company's U.S. location, may scare away customers who want to protect their privacy.