I have seen AVG on Windows machines and haven't been impressed. Pushy, too many bolt-ons etc
On mac, I use:
ClamXAV, not in real-time mode, but for drop'n'scan for downloaded files
LuLu 2-way firewall
Knock Knock, BlockBlock to check & remove if any unauthorised software tries it on...
Reikey keylogger detect
SilentKnight to check status of SW updates