AntiVirus Software: avast! 1, NAV Nil

I have been a loyal customer of Norton AntiVirus (NAV) software for many years, largely due to factors other than the primary function.  More due to luck than skill, I have experienced very few virus issues.  When asked for recommendations, I typically would suggest NAV as a 'safe bet'.

A few years ago, I began to run into an increasing number of issues, ranging from incompatibility with other security software (specifically ZoneAlarm), performance impacts, LiveUpdate failures, difficulty upgrading NAV to current levels, and, the last straw, NAV failures that would block Internet access.  Often, recovering from these problems was time-consuming because NAV would end up in a state where it could neither be uninstalled nor repaired.  In the end, I had enough and looked for alternatives.

I settled on avast! based on high marks from antivirus rating services, user reports, reasonable pricing (free is always nice) and Vista support.  Installation and configuration was painless, guided by the tutorial How to Install, Configure, and Use Avast Antivirus.  A minor incompatibility with ZoneAlarm Pro was easily resolved.  A Pro version of avast! is available at a reasonable cost, providing a few additional features like scheduled scans.

I recently had an opportunity to compare avast! and NAV in terms of function.  A few months ago, I was asked to diagnose a PC with intermittent performance issues.  NAV 360 had recently been installed on the PC and a full scan did not show any problems.  Based on other reports of NAV 360 performance issues, I removed NAV 360 - the performance issues disappeared.  During the install, avast! reported and quarantined three files flagged as adware or trojans.   Last week, I helped clean up a PC that had been infected with a variety of  trojans.  Again, NAV  neither blocked them nor found them during a full scan.  On the other hand, avast! found and quarantined 16 files as malware. 

A very selective sample and Your Mileage May Vary, but I think you can guess how I will respond if anyone asks for a recommendation on antivirus software.