The first rule of thought for the most is no one program will ever cover 100% of the "bugs" out there. Along with AVG here I also add layers of protection with other free programs to see how well those will do.
For testing Spyware Terminator I can now give that one a clean bill of health! Upon intentionally allowing active x controls to install upon receiving a spam mail ST sprung to life to allow or block what was to follow. Sure enough not only the Smiley Central toolbar went when allowed but a backdoor trojan and a few other nasties!
Upon seeing that the ST scan found some 338 items to remove. But allowing the backdoor bug in and then cleaning off the crud with the scan saw IE 7 made toast! A system restore point was then needed. ST had done it's job however!
http://www.spywareterminator.com/
That one does far more then Ad-Aware. Kaspersky is definitely a good product along with a few other retail products. I can't AVG lacks the ability to detect things. Even with AVG totally disabled in the msconfig utiltiy's startup and services groups I've seen it come to life out of nowhere upon reaching an unknown site during a search where a trohan was instantly copied to the drive. AVG sprung up and pointed out the file name and location.
Norton and McAfee are usually found on the foobar list regardless while even the free versions by Grisoft and others seem always preferred by most. The key however is seeing more then one type of program put inplace to add the actual "layers of protection" over counting on just one entirely.