Free antiviruses compared - AVG vs. Avast vs. Antivir

Well, I tried all three of them in the real work environment.
For the last couple of years I was using AVG and it worked good for me.
Once configured, it smoothly run on background doing it's job.

However, for the last 6 months or so I noticed that my Thunderbird (2.0.0.23 at the time of writing) was getting slow. It was slow on emails download, on emails browsing and on emails delivery. I also found that 1 of my 4 Quad CPU cores was at 100%, executing one of AVG child processes. I tried to re-configure AVG or re-install the newest version from the scratch and I looked for anything wrong with my Thunderbird configuration, but was unable to find any clue.

Additionally, I noticed that the latest free AVG 9.0 won't auto-update anymore. It requires manual update, which is obviously a serious problem for busy people. I can not remember that my anitvirus is not updated and AVG 9.0 even does not notify me about that.

So I ended up removing AVG after being their user for a long time. Now the options were Avast! or Antivir.

I installed both in parallel on a test computer, just to let them breath for a while. I am glad I did that since after a few days I removed Antivir. It could be a great piece of software, but it's German creators decided to show you a periodic reminder (daily or may be once in a few days) that the paid version gives you more protection. So the first thing you see when you open your computer is a big pop-up window "buy Antivir". Thank you, I removed this nice auto-reminder software when I got the second "buy now" message.

Thus I am with free Avast! antivirus now. Avast! works good with my Thunderbird, all my email issues gone. Emails download is fast and Thunderbird never freezes up anymore on emails browsing or deletion. Like all the others, Avast! has it's own weird stuff, like the default voice notification 'virus database is updated'. Fortunately, sound can be switched off through Settings->Sounds->Disable Avast Sounds.
A few more annoying things that I yet did not found how to avoid yet include:
- small auto-closing pop up notification window on auto-update. I do not want to see it.
- pop-up if an infected email arrived - I would like Avast! to take a default action (delete the attachment / virus in my case) and never show me any window.

Anyway, at the moment Avast! is the best choice for my environment.