I used AVG free for 3 years (also trialed 7) , but found through various testing that avast detected more than AVG.Another plus is that when ive submitted files to avast that hasnt been detected ive had a reply and the updates have been within two days.This forum is also excellent for help and many alwil people post here too.I also for a while kept AVG on my computer as a backup (resident shield obviously not running but as an on demand scanner),but have now come to the conclusion that AVG offers no benefit over avast and use just avast.For a “second opinion” i now use kaspersky online as it is widely regarded as one of the best trojan scanners too.
http://www.kaspersky.com/scanforvirus
It is however not a complete scan but files up to 1 meg can be uploaded.
me