Been using the free ZA since long before I started FFXI, never had any real problems with it other then needing to whitelist a site or subnet if it was getting blocked, but that has only happened a few times. The log tells you the IP and port ID of what got blocked, so when it did block FFXI's new IP's last year, it was easy to tell what was going on and fix it by just adding them to the safe sites list.

Symantec stopped releasing updates to the Corp. Edition I had been using for years, which really sucked as it was the least intrusive one they ever released and it never gave me any trouble with my games. They started pushing everyone to that slow .Net driven 360 crap that just eats system resources, so I took a chance on Avast 5.0 about a year ago and it's been a decent freebie. Will want to add the FFXI folder to the exception list though, as it (like others) has been known to give false positives on FFXI with some engine updates. Only real glitch I ever had with Avast was an issue with PowerDVD, but support worked with me and Cyberlink and after about 3 weeks, we tracked down the culprit and they pushed an update out a few weeks later that fixed it for everyone. Was pleasantly surprised with how well they communicated with me on that--even relayed an issue with my Asus card to Cyberlink and they got me a patch to fix an issue I was having with theatrical sound on my Blu-Ray playback. Not too shabby for a free product.