I started working in the IT industry in 1974 and I'm still with that same company. I sold many antivirus programs over the years. I believe avast! is the best antivirus bar none! I haven't had a virus spread through an avast! protected network in the 9 years I have been selling and supporting avast! I have replaced Symantec, Norton, McAfee, AVG, Komodo, and MSE due to a virus spreading into every computer on customer's networks.
This is the number 1 I.T. nightmare. I have never had this happen with avast!. This should be the main criteria, in my opinion, when choosing an antivirus program.
There is no perfection in our industry, and there never will be. Every program has it's idiocracies. The best A/V programs, on average, stop 95% of virus, and 70% of spyware.