Comodo has been getting good reports, so give it a go. If it causes problems, you can just uninstall and try another brand (rebooting in between).
Don't forget anti-spyware programs too for weekly scans etc:
A-squared free
http://www.emsisoft.com/en/software/free/
AVG Anti-spyware (full version 30 days, then you loose resident shield, and automatic updates. Still effective as you can download manually, and uses same malware signatures)
http://www.ewido.net/en/ (used to be Ewido)
http://free.grisoft.com/doc/1
Spybot Search & Destroy
http://www.safer-networking.org/
Adaware SE Personal
http://www.lavasoftusa.com/software/adaware/
could also try Winpatrol:
http://www.winpatrol.com/
once setup( (takes less than 5 mins to create the rules) it is hardly noticeble, and alerts you to new starup items etc. Also has a cookie manager for IE, which is handy.
All the above are, or have free versions.