I'm trying to do a bit of research myself, trying to pick one of these options:

1) AVG free - currently using

2) Antivir free + Spyware Doctor Starter edition

3) ZoneAlarm Internet Security.

I've already got ZA, just that I've disabled the AV for AVG since 2 years ago, Mind you, back then ZA was using the CA antivirus, which is quite an appalling AV app. The current ZA antivirus engine is a built on the Kaspersky SDK, so it's slightly inferior in therms of functionality, but not definitions. (Still, it translates to a smidget lower hit percentage).

What's making it hard is everybody's reviewing the paid versions, people assume ZA's AV is my Kaspersky, so "it must be the same", while others just don't have any credibility at all.