Stick with Avira free, Avira premium is only a trial version.
http://www.free-av.com/en/products/2/avira_antivir_premium.html
http://www.free-av.com/
Spybot - Search & Destroy and Ad-Aware and not that good. Instead Install and weekly or so update and run a full scan with:
Malwarebytes' Anti-Malware free version
http://www.malwarebytes.org/mbam.php
SUPERAntiSpyware Free Edition
http://www.superantispyware.com/superantispywarefreevspro.html
How To Remove Malware For Free
http://www.youtube.com/watch?v=8Ah3efRdWes&feature=channel_page
Uses only Avira, Malwarebytes' Anti-Malware, and SUPERAntiSpyware to remove most malware.
==================
Optional, also install:
"SpywareBlaster" (free) , Update, and Enable all protection
Blocks about 12,000 items
"Spybot Search & Destroy", update and immunize and scan. Immunize blocks about 120,000 items
Disable tea timer and SD Helper:
Mode > Advanced > Tools > Resident > Uncheck "Tea timer" and "SD Helper".
====================
Good free online scanners; Run a different one each month or so. Rotate through the list.
"BitDefender Free Online Virus Scan"
"ESET Online Scanner"
"Kaspersky Lab Free Virus Scan"
"McAfee FreeScan"
"Panda ActiveScan"
"Symantec Security Check"
"Trend Micro HouseCall"
"Windows Live OneCare Safety Scanner"
===================
If you want to be 100% safe from malware while surfing the web install Sandboxie. Per Sandboxie "Sandboxie runs your programs in an isolated space which prevents them from making permanent changes to other programs and data in your computer. " You can right click on any program icon to run it in Sandboxie. If will automatically set up to use your default browser.
Sandboxie (free)
http://www.sandboxie.com/
In Sandbox settings:
Sandbox Settings > Delete > Invocations > Check "automatically delete contents of sandbox"
(see video below)
Video of Sandboxie. Installation and use, (Part 1 of 3 parts)
http://www.youtube.com/watch?v=GueXMq-Vyi8&feature=channel_page