I did a search for firewall threads and this is the most current "which is best thread" I found in Networking, so here's a little service to help you guys out...
I'm actually in the same boat as you in that I'm looking for the best personal software firewall I can find (that's free, ideally

). I searched the popular firewall developer sites and found this
comparison chart on Agnitum's (maker of the Outpost firewall) site. The chart lists 28 features of firewalls and compares the most popular firewalls (even giving links to each competitor) against those features, giving each firewall one point for each feature it did have. Surprisingly enough, the Outpost Pro ($40) firewall didn't even get a perfect score (got a 26/28), so that seems to mean at least Agnitum is honest about their comparison and not only comparing on the features that they do have.
While I'm now considering purchasing Outpost Pro, I'm going to evaluate Tiny Personal Firewall because it was the highest scoring FREE firewall on the chart.
I found this chart very helpful... hopefully you guys do also.
EDIT: Here's a good article on firewall comparisons from PCMagazine.