when my norton subscription ran out i had problems renewing online so did a bit of research. it would seem from reading all the reviews of av software that none come out great but in the end i went for panda titanium 2004, picked up an oem copy from a well known auction site. it found a couple of worms strait away. in my experience 'free' programs are not as thorough as ones u pay for. eg pest patrol is a far superior product to adaware 6.
There probably isn't a "best antivirus program". If they all do the job they are supposed to then any one of them is the best. Some you pay for some you don't. I used to have McAfee AV on yearly subscription but have been using AVG (free) for a long time now, does exactly the same job and does it well. Get AVG from click here