Here is another strong vote for MSE.
If you read technical articles, then the names Fred Langa and Paul Thurott may ring a bell.
They, like many of us here, use exclusively Microsoft Security Essentials, MSE.
they also use Windows Defender Offline (WDO) as an "offline" scanner.
Your will find links to both in my signature.
Here is a link to an article from a Security blog which I recommend reading. Understanding Microsoft Anti-Malware Software 2012 ~ Security Garden