AV programs and suites trade position frequently in reviews of what's best at any one time. My choice has been a suite (paid for) that stays consistently near the top in the ratings, but others may choose to switch about as the threats change.

If you're going to look for good protection, especially in free-ware, it's good practice to check fairly frequently whether your current choice has continued to be a best choice for your needs.

Without recommendation, here's the most recent I've seen in a review by a fairly reliable source:

Lab Testing Antivirus Software, 02.04.10, Neil Rubenking, PC Magazine.

Only 8 AV programs/suites are reviewed, so it's not an "all inclusive" review, but there are comments on some of the more popular ones people here are using that may be of interest.

John