Windows Firewall
This is my number one choice and is the only firewall I use on all of my machines. It is very low on resources and, unlike other firewall software, it is not very invasive.
Being made by Microsoft and embedding into Windows makes this an ideal contender, it knows how Windows should work and it has a better knowledge of what to look for when malware tries to attack your computer.
There is one downside though, if malware were to infect your system (very unlikely), there is no outbound connection monitoring meaning anything malware records can be sent to the hacker for misuse, such as confidential information etc...
Overall though, with its low resource use and it seemless integration into Windows, it makes this my recommendation for the average home user.
