As far as Anti Virus scanner are concerned the simpler the better really. THe problem with most of these programs is that they serious bog down your computer because there always doing some kind of crap in the background.
Up until recently I used AVG free that was a simply light weight antivirus, but alas they bogged it down, and its just not the same anymore. I now use Microsoft Security Essentials. Its free and does the job without harassing me every two seconds, and eating up all my CPU cycles. Any program that has a billion different parts to install is inevitably going to run a bunch of crap in the background, and bother you every two seconds.
For years before that I ran nothing at all because I needed all the performance my computer could give me, these days though that inst such a concern. I have never had a virus on my computer. The best defense you can have is practicing safe web browsing its really as simple as that. If you know where and what your doing and not clicking on obviously infested links then there is no reason for a virus to ever get on your computer.
The majority of the AV products out there are bloated and just going to make you frustrated and drain your wallet. The simpler the better is my opinion and just keep in mind what your doing when your browsing the web.