Other - LnS. Simple, plain firewall without fireworks like HIPS, very light for resources. Also having one forces you to study about how FW works since it's rule based firewall and needs knowledge from user when it comes to create new rules
Online Armor but, like any software firewall, only when used behind a hardware firewall (usually a router). I must state that I like Outpost just as much as OA; I am using OA because it is easier to use. Acadia
Outpost when I want a FW with HIPS, otherwise Windows Firewall Control or Sphinx. I'm going to trial Jetico pretty soon and also Comodo All other FWs annoy the hell out of me.
Re-formatted my machine, using Outpost Firewall Pro again, no more problems or bugs either. I'm using it because of it's outstanding features and It's overall effectiveness + strength as a firewall.
I'm using the fw that is included w/ Kaspersky IS. It seems to not cause any problems and I like the extra feature of blocking banner ads.
Voted Outpost and Other. Outpost Security Suite on my Windows installations, because I like it and have been using it for years, plus I have a lifetime license. I don't really need it, I only run Windows in a virtual machine. Other; which basically translates for me to None. Unless you want to count by router.
A good mixture of responses and its nice to see the native windows firewall is becoming more popular.
Comodo FW D+ suits my needs and tastes perfectly. OA used to fit that bill, until I ran into problems with it and other programs I use, so I switched. Glad I did.