I have tried several anti-virus, and they all seem like a mix bag. I have tried Norton (missed a lot of stuff), AVG (was free, used it for 5 months, then got a really bad virus it couldn't deal with) and Pervex, more of a scam then a program.
Eventually tried Cyberdefender, and have been happy with it now for about a year because:
I liked its user interface, and easy to use, which was good when my kid was on the system and he hit an infected site - Cyberdefender walked him through it.
It found some viruses and spyware that I knew was on the system (AVG did not find them), and took care of them (I used the paid version of Cyberdefender - the free version is only a scanner).
Protected me from some funky virus when I hit a blog that tried to take over my browser.
The paid version comes with 24/7 computer help. My experience with them was very positive, not pushy, just trying to help, was able to to determine that one of my ram modules was bad, and how to fix it. Total cost was much lower then hauling the system to Best Buy so they could keep it 2 weeks and overcharge me.
JMHO