Which of the following tools would be the best choice for achieving compliance with PCI Requirement 11?

TrueCrypt is a disk encryption tool used for data-at-rest protection, not a vulnerability scanning or security testing solution relevant to PCI Requirement 11.

Sub7 is a remote access trojan used maliciously for unauthorized system control, and is not a legitimate compliance or vulnerability assessment tool.

Nessus, developed by Tenable, is a widely used vulnerability scanner capable of performing the internal and external network scans required by PCI DSS Requirement 11 to identify security weaknesses. It supports authenticated scanning and compliance policy auditing, making it a standard tool for meeting Requirement 11's regular security testing mandates.

ClamWin is an open-source antivirus application focused on malware detection, not the vulnerability scanning and penetration testing required by PCI DSS Requirement 11.