Any suggestions as to the best site for downloading antivirus software?

When it comes to antivirus software, I believe you should not go cheap (aka free). Free products ARE better than nothing, but commercial products, in my opinion, have better chances of success and better chances of catching newer viruses.

Which would you rather, go to a doctor with 6 months experience or go to a doctor with 25 years of experience? I want the experience so my chances of being misdiagnosed are far less.

For business, I recommend McAfee. For enterprise environment, McAfee Enterprise Edition is a great product that is highly manageable and easily installed. McAfee has been making quality antivirus software for at least 20 years - they generally know what they are doing. I've used them in a large environment before with almost ZERO conflict with any installed program (the one exception I can recall was Corel Easy CD Creator in the mid 90's). They update virus definitions quickly and in my experience, a well updated network running McAfee will have a very LOW chance of experiencing a virus outbreak.

For business, I DO NOT recommend Symantec. While things may well have changed in recent years, a few years back, I tried installing a current version of Symantec Antivirus Corporate edition on a Windows 2000 Terminal Server 6 months after 2000 was released. Symantec did not support terminal services. McAfee had been working great on terminal services EVEN IN BETA VERSIONS OF 2000 for months prior to it's release. (I'm sure the current version supports Terminal Services, my point is, I find it difficult to excuse their slow progress in keeping the product compatible with current technologies). A couple years later there was a couple of highly publicized virus outbreaks. My company was hit with one the day of the outbreak early in the morning. By midafternoon, McAfee had definitions to remove the virus. Another company I consulted for used Symantec. They were hit as well and they used Symantec. Symantec took two days to release a non "beta" definition file - they did release a tool to clean it - MANUALLY. Had we used Symantec at the larger company I worked for it would have required hundreds of man-hours to clean the systems using the manual symantec tool. McAfee covered us in hours.