I would avoid McAfee, Norton....if you find the free ones burdensome w/o the update features.....or just want something better, it's hard to beat the following:
ZoneAlarm Security Suite 2010 for 3 PC's - $39.95 ($13.32 per PC)
Includes ZA Firewall, Kapersky AV and AM, Parental Control, AntiSpamhttp://www.zonealarm.com/security/en-us/zonealarm-computer-security-suite.htm
F-Prot AntiVirus for 5 PC's - $29.95 ($5.99 each)http://www.f-prot.com/products/home_use/win/
I have been using F-Prot since 1992 and ZA Suite for about last 6 years. ZA is firewall / active scanner and F-Prot does nightly scans.