I don't think I have ever heard anything as well articulated than that moonlit.
IMHO if you want GOOD antivirus protection, you need to pay for it. If you will to have some protection, but not the most up to date definitions, than go the free route. If you don't care because you format your HD every 6 months than forget the AV shit.
But just remember, the best anti-virus software won't protect you against stupidity. watch what you download and torrent and for the love of god, use a web-based e-mail client like gmail.