VPN Protocol Comparison : PPTP vs L2TP/IPsec vs OPENVPN vs Chameleon

PPTP: very low security, fast speed
L2TP/IPsec: medium security, fastest speed
OpenVPN (128-bit BF): medium security, fast speed
OpenVPN (256-bit AES): highest security, good speed
OpenVPN (128-bit AES, ECC): high security, fast speed

PPTP is insecure but it works on most Operating Systems/devices by default. It is very fast in our implementation, but since it's not as secure as other protocols, we recommend to use it only for activities that are not too sensitive (i.e. to unblock geo-restricted content).
L2TP/IPsec is secure and arguably the fastest in our implementation. It's not as reliable as OpenVPN over networks experiencing issues, leading to connection drops.
OpenVPN is the most secure and reliable (even over slow/unstable networks).OpenVPN UDP is faster than OpenVPN TCP. OpenVPN is also harder to block by ISPs since it also runs on standard ports like 80, 53, 443.
Encryption strength
PPTP: 128-bit MPPE
L2TP/IPSec: 256-bit AES (with Maximum Strength Encryption enabled in manual setup or with our software)
OpenVPN 128-bit BF: 128-bit BF-CBC for data channel, RSA 2048 for keys and SHA1 HMAC
OpenVPN 128-bit AES: 128-bit AES-CBC for data chennl, RSA 4096 for keys and SHA256 HMAC
OpenVPN 256-bit: 256-bit AES-CBC for data channel, RSA 4096 for keys and SHA512 HMAC
OpenVPN ECC: 128-bit AES-CBC for data channel, Elliptic Curve using curve secp256k1 for keys and SHA512 HMAC
OpenVPN XOR: 128-bit AES-CBC for data channel, RSA 4096 for keys and SHA512 HMAC

OpenVPN XOR is similar to OpenVPN 256-bit in terms of key strength and HMAC as the same are used, it is just the symetric cipher that is different, AES 128-bit being faster and less CPU intensive than AES 256-bit.

Πηγή : https://vpn.ac