I heard that BitDefender Antivirus Plus 2013 is a great antivirus. It is highly effective. There are some people having issues with scan times, but their real-time protection is great, and they rarely give out false positives. Internet Security is basically Antivirus Plus with a firewall, but Windows 8 comes with a free firewall. The firewall that comes with BitDefender is a great one, though, and it has many options. Their 2013 editions are also Windows 8 compatible.
However, if you really need faster scan times in exchange for a little accuracy (it's all about balancing the two, y'know), you could try Kapersky Antivirus. I've had speed and RAM problems with Norton in the past, but I'm not sure about the latest questions. So it's either BitDefender for accuracy or Kapersky for a bit more speed. I am a happy BitDefender user, BTW.