Avast is so much better ^_^ AVG doesn't allow me to do many things with my online apps, while Avast is better at picking out what is actually a threat. Avast has many more options and the user interface can get no friendlier to the user. It tells you with alerts and sounds when something important happens, unless you tell it not to. Also, the scan has never failed to pick up a virus and stop it. If the regular scan doesn't work, boot scan will. There are numerous skins to make Avast easier on the eyes.
The best thing for me, though, is that it is a complete package. Only antivirus? I think not. I have no firewall. I have no antispyware. Avast Antivirus's web scanner and resident scanner acts as both together!
I use Avast Pro Edition and I will always ^_^
~~Ben