Quoting myself on a different thread:
On AVG Antivirus, I realize that many people are happy with this, particularly the "everything on the Internet should be free" crowd, but the product does _not_ test out well. Here is the industry standard site for AV testing:
Virus Bulletin.
Drill down to "by vendor," and you see that Grisoft (aka AVG) gets a rather astounding 3 passes/19 fails. In fact, before the last two tests they were batting 1 pass/19 fails!
Norton has passed 16 times in a row at present.
Panda hasn't submitted in a long while, but was 1/3 back in 2000-2002.
Comp.Assoc. has passed the last 7, and 16 of 17.
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As for Maximum PC's rating, I haven't read that yet, but their reviews tend to be pretty lightweight.