I have used a variety over the years.

Started with Norton but found it missed too many threats that others picked up, such as AVG, Trend Micro online, Panda Online.

I have used Zonealarm but it went all funny on me too, so now I use the free program from my cable company. It includes a firewall that is awfully similiar to zonealarm, and has the professional ad-aware with it, plus a robust anti virus program that seems to work fine.

I also augment it with using the panda and trend micro online scans regularly for safety sake.

just my 2 cents
Ian