I used to use free ZA but too many problems with AH. I switched to free Sygate and no problems at all. TPF is also good. Check this liink.
http://grc.com/lt/scoreboard.htm from Steve Gibsons Leak Test.
LEAK-PROOF (SAFER) PERSONAL FIREWALLS
Firewall Considerations, versions, etc.
McAfee Firewall v 2.15+ — Update to get version 2.15 or later
Sygate Personal FW (FREE) v 4.0+ — FREE for personal use!
Symantec / Norton v 2.55+ — LiveUpdate to get version 2.55
Tiny Personal FW (FREE) v 2.0.7+ — FREE for personal use!
ZoneAlarm (FREE) Never Leaked
ZoneAlarm Pro Never Leaked
DJ229