What is the best firewall?

Leaving open gaps in a firewall exposes the protected system to malicious abuse. Obviously, a fully closed firewall would prevent applications from accessing information on the other side of the firewall. Thus, it is necessary to carefully open small holes in firewalls that are very small and restricted (hence the term pinhole). For best protection, the mechanism for opening the pinhole in the firewall must implement some form of validation and security that will protect the system behind the firewall.