Free stuff and our computer got infected regularly. AVG came highly recommended, but malware still found it's way in.
If malware is finding its way in "regularly", you're doing something wrong. Seriously. There just aren't that many *remote* 0-day exploits (vulnerabilities with no known fix). In other words, either you're computer is woefully unsecured or one of its users is... f*cking things up

If you start out with a clean system, malware has to come from somewhere. Who's downloading crap?
You might also want to take a look at what browser you're using and what plugins you have installed.