I've been using the beta of MS's Security Essentials since it came out in my win7 beta and I've been very happy with it. I have tested it a couple times with sending in virus signatures in various ways and it's caught them all. I'm not actually worried about getting a virus myself because, well I'm not dumb. So it's more about preventing oops' if my wife is using the computer of if I'm needing to trouble shoot someone elses harddrive etc...

So for those reasons I want an anti-virus software that doesn't hit the system resources badly and MS really is pretty light weight in that dept. It is far less of a hog compared to AVG and I've never personally liked Avast so I can't directly compare it.

Normally if I was just needing a scan on demand anti-virus only I use clamwin. However because I do want some real-time scanning for oops protection I will be using Microsoft Security Essentials from now on. I'm quiet happy with it's performance and feel comfortable with it's security.

Plus the dinks at Symantec have said it's horrible, useless and generally prone to horrible failure and no one should ever use it. Given their track record that's an awesome recommendation in my books. The whole enemy of my enemy thingy.