i find avast spot on (and free )
No antivirus can stop today's malware on it's own. They are simply changing too fast. For complete protection you need something like Comodo Internet Security which is totally free. http://www.comodo.com/home/internet-security/free-internet-security.php
I use Avira.
My norton had 1 day left so i have just un installed it and downloaded ms security essentials, norton slowed the laptop down so bad.
Hopefully ms will be better
I use both of these, works a treat. Been using them on Vista for 2 years now (Same install) and had no issues! (Also no BSOD, wahey)
I use linux.