I am of the firm impression NOTHING can compete with the Ewido system. It has saved my system from stuff Norton and AVG went tits up over. You can get a free trial for two weeks from www.ewido.com
I use the Norton Internet Security package and think it is OK on the work computer. On my desktop at home I run AVG, Zonealarm and the Microsoft Antispam scanner tool - works fine for me on my Win2K Server setup.