I think the freebies work well. My wonman uses one. I ran off to buy a paid for version when I caught a virus despite a free one a few years back though. Can't be sure if it is better but I'd like to think I'm not paying for nothing :-)
Avast free anti virus for me, never bought one and never will, even the ones that you pay for have their problems. If you scan say once a month and use something like malware then the freeies are good. In my opinion.
Microsoft Security Essentials .. if you're worried about paying : )
Just the bare NAV 2012 if you're not. Best I can find is £16.00 for 3x PC's for 1 year.