I get this question a fair amount. Here is the latest version from someone on Facebook: “To all the computer wizards out there: Which antivirus do you suggest putting on a computer?” My response…
Short version: Spend your money on backups instead.
I think I am in the minority in the industry on this, but I tend to recommend “none”. Antivirus software is a bit like insurance. You are going to pay something (dollars, at least some slowdown, and potential problems) all the time to potentially avoid paying a big something later.
No antivirus software can completely protect you from reckless behavior, and if you’re responsible, the risk is probably acceptably low. By “responsible”, I mean things like: don’t open attachments or click on links you were not expecting, regularly apply updates to your OS and browser, and only install software from trustworthy sources.
For the typical home user, the cost of recovering from a virus is pretty minimal, if you have backups. That is where you should focus your energy and/or money. And always test your backup method to make sure you can actually get your files off of it!
Update: Running Microsoft Security Essentials is probably reasonable. It’s free; you get it as part of Windows Updates.