In my experience, the anti-virus programs are six/half. Most people qualify for some kind of partner-subsidized subscription to one of the large commericals, for example I get McAfee for free through Scottrade. Make sure you also have a firewall of some kind. Last but not least you will need an anti-spyware/trojan program like Malwarebytes. After my last infection with the "Security Tool" trojan & rootkit, I paid $25 for the Malwarebytes lifetime premium sub with real-time protection and IP blocking, worth every damn penny. Haven't been infected since and I frequent all the usual suspects.
Had a discussion with a software professional who had switched over from anti-virus programs to programs like "Spybot" and "hijack.exe" to protect their computers; things have been really good with almost nil attacks.