What Antivirus Program Uses The Least Resources?

I use F-Secure and I love it! No complaints, no reason to change. It has never said it couldn't remove something but then very little gets by it in the first place. I have been recommending AVG to friends who don't wish to fork out cash but I have been noticing that most people who are looking for help with viruses are using this or NOrtON. AVG does not have real time scanning after trial is over. I think I will start recommending Avast to them after I look into it a bit more. I would like to prevent a virus from getting on in the first place rather than having to remove it. Practice safe browsing habits. Don't open email you aren't expecting or from people you don't know. Scan attachments b4 opening even from friends. I use IE7 and Firefox but just came across an add-on for Firefox called NoScript which seems to work excellent. So I will probably just use it except for windows updates which must be used with IE. Firefox also has a rendering engine add-on for use with sites that only want to work with IE making it possible to use Firefox on those sites. My computer came preinstalled with NOrtON and I cannot get over how much faster my computer is now compared to then. Another reason I personally didn't like NOrtON is because I accidentally denied access to web for a program once and had a real problem reversing it. HPs' solution to this was to do a restore as they couldn't figure any other way to reverse it either.