Just in case anyone was getting the wrong idea, AVG Free doesn't nag you... unless you call the little ad banner under the main scanner window a nag, or asking you maybe once a month if you'd like to upgrade. Although it has gotten a bit more bloated in the last few releases...
MS Security Essentials I've stayed away from because I've seen a few issues with it not updating, not launching properly. However, those were probably due to the customer's "money-saving" having only 256MB RAM with XPSP3 and multiple windows of office, IE, etc open. 2GB and he's good to go, but I had to tinker with his services, I think because Windows disabled some of them so it could breathe. So, everyone thinks that it's a great AV.. good detection rates, all that?