I have 2 computers and have one on zonealarm and one on kerio. Personally prefer Kerio it has a nice interface, comes up with a few windows when i use a new peice of software and asks what i want to do and thats it, you can also setup a user friendly install where no windows pops up and kerio is just in the background. Now zonealarm on the other hand really annoyed me, i went to open my EVE game and it instantly blocked it with no choice if i wanted it to or not, i then had to hunt through the horrible interface to find how to allow the access again
Also when u install the Kerio firewall u are getting the full thing as if u have bought it, although this only lasts for 30 days and then reverts to a simple firewall for free. But i think i am actually going to buy it becuase apparently i can get it for $9.95 a year which i think is just so cheap it would be daft not to buy it.