I had used AVG Antivirus free long time ago for a long period before USB infections started to propagate. Then I switched to Kaspersky Antivirus and then Kaspersky Internet security. Now I am back at AVG Internet security. Now The Internet Security is a whole package including Antivirus also, but Antivirus is just Antivirus with less features which might not protect you from malwares or spywares fully.
System Shield provides everything you need to completely protect your PC. System Shield comes with a number of tools as following:
iolo AntiVirus Which detects, blocks, and removes viruses, rootkits, worms, trojans, and other dangerous programs with always-on protection.
iolo Personal Firewall blocks unwanted communication to and from your PC, keeping your private information safe from hackers and identity thieves.
Spython™ AntiSpyware removes spyware parasites to protect your privacy and prevent system crashes and slow-downs.
Security Optimizer repairs dangerous security vulnerabilities that would otherwise leave your system open to attacks by intruders and data thieves.
SystemGuard locks down your system configuration to prevent unauthorized changes by spyware, viruses, malicious Web sites, and remote attackers.