Well I'm sorry to hear of you negative experience with Avast.
Me and hundreds of other people I know have never had a problem with it, you seem to be the exception.
Avast was rated number #1 and
"having excellent virus and spyware detection rates according to antivirus test results from AV-Test.org."
http://freebies.about.com/od/securit...-antivirus.htm
AV-Test.org is an independant virus testing lab.
http://www.av-test.org/index.php
The two worst antivirus programs I ever had were; NOD and Norton. They both infected and corrupted my system.
They also chew up ram like crazy. Avast is easy on resources and it updates atleast once a day its virus database.