The Microsoft one is excellent. I use it and it seems to work really well. The other thing i do is run some adaware/spybot software. Also once a month i use an online virus checker such as bitdefender to run an online check. That way it picks up anything that my installed virus checker doesn't get. Which sometimes it does get something since some viruses are tailor made for a specific antivirus program to avoid detection.
Other things to do:
Never run your user ID as administrator. set up new id's with passwords can be a huge help.