Like most security suites, these versions contain the same core engine and features, but when you upgrade to the various paid versions you get additional features. The free version contains the main antivirus and antispyware engine, detection but not removal of rootkits, Netbook support for low-resolution monitors.
-1, That right there is a major disadvantage compared to other free avs.
There's scanning tech that can crack open "locked" files
+1 That seems useful since Avast! can't scan password protected files.
improved internal security to prevent AntiVir's files from being maliciously altered
Avast! already has I believe
and one-click threat removal--baby-sitting was taken out in the last version.
Avast! has automatic removal options now
In addition to those features, AntiVir Premium 10 introduces antiphishing protections, a download blocker to stop unwanted ''drive-by'' downloads, an e-mail scanner, Web guard, rescue CD creator, and a behavioral engine tuned to unknown threats.
-1, Avast! Free already scans emails and websites, and scans downloads anyway, and it has behavior monitoring.
I'll still stick with Avast! but I would probably switch to Avira over AVG.