We've tried a number of antivirus programs over the years. The one we found that was the least intrusive, and had the best interface was from GFI, and is called "Vipre". The enterprise/business version (Vipre Business) has a lot of features that make it the perfect fit for today's corporate environment.
For home users, we just cannot recommend the basic "retail" antivirus bundled with most new systems. The great news is Vipre is also available for home users!
P.S. - It is always good practice to check the virus definitions to ensure it is updating correctly.