At least in terms of leak tests the paid version of ZA is fairly good but not best. The free version of ZA rates very poorly.
From somewhat older leak tests that dated enough to not include comodo version three, the top two rated firewalls were the Agnethium paid and the on line armor free. But on line armor free and comodo free version three are both bring out new versions and revisions at a rapid pace.
The some what radical departure adopted by both online armor and comodo versions 3.0 and greater is in combining an excellent almost leakproof firewall with HIPS and process control functions. That plus whitelists end up making both firewalls almost self configuring on most computer systems. But I do expect that will be the firewall trend of the future as other companies play me too. And with the plethora of new versions coming out, it will likely be a long time before unbiased third party testing sites can be up to speed on comparative versions as new versions come out faster than they can be tested.