it will depend of what type of user you are, however i may tell you that if you are in your home all time and doesnt go out too often you my dear dont need a firewall as most of the modern routers (no modems) have a built in firewall or at least they use NAT (which is not a firewall itselft but it can be compared to one), but if you connect to public places you surely will need one.
I will talk about free stuff....
if you are an expert user and go to public places:
Comodo is the best option for you, despited the fact that most of the user complains about the buggy software it became recently is by far the best FREE sol you can find there... also please notice that if you set up properly you can get just a few notifications (and not thousands). I may say that comodo product is intended for everyone but i listed here as an expert option due the powerfull tool that it provides. It is just a complete fortress. BUT if you dont know what to do with their settings you will have a bad time XD.
PST: comodo itselft wont slow down your pc
if you are a middle user:
Private firewall is an excellent choice if you are a middle user with some knowledge of security, however this soft. can be considered as an expert choice, why? the answer is this one "only the developers know how to handle their settings xD" . There are 2 cons:
a) you will see a pop up from time to time asking about some stuff that you need to be careful ( i may suggest to turn off HIPS at all) but if you turn off some modules, you will see a window once a while
b) some times it may free (at least in windows 8.1) and this could be a problem because the GUI would just freeze for almost a minute
if you are a norma user (that doesnt care about security and doesnt mess around)
Zonealarm firewall will be an excelent choice, it wont ask you too much stuff, but there are some cons:
a) it may include some PUP bundled with their installer
b) in some modes it may not stealth ports correctly and may leave some open.
this is a firewall that covers the basics