Hi
This is a good place to start
PC Safety and Security--What Do I Need?
I've always used free versions and never been infected. Of course, careful surfing habits are essential as well. In general terms, the paid AVs usually have some kind of support line available and they do tend to update ahead of the free versions, but as long as I receive updates then I'm happy. In the above article, you'll also find a link to a site that reviews all major AV programmes - let's you know who is doing best in terms of detection etc - allows you to make an informed choice. While I have never use McAfee I have seen users who say it slows their system.