According to leaktests ZoneAlarm Pro is actually good, although not the best. ZoneAlam free is lousy however.
http://www.matousec.com/projects/win...p#result-table
The top contenders are still Comodo, Jetico and Outpost Pro, but now there's Online Armor, which I hadn't heard about. Anyway only this Online Armor and Comodo are for free, the free versions of Jetico and specially Outpost are much poorer.
http://www.matousec.com/projects/win...ewalls-ratings
Anyway these tests are about outbound protection, which is relevant basically in the case that the computer has already been infected. Also outbound protection means that the firewall will be asking the user, and that's not for everybody. But if someone doesn't want this but inbound protection only, he'd better leave the Windows firewall.