Through all my searching most posters recommend Avast. From what I understand it's small, not intrusive and windows friendly. But I'm unfamiliar with it.
Before using MSE (after a format) I used Comodo
and had no problems. That's what I've gone back to. It's free version is anti-virus only and just a heads up when installed it will install Geekbuddy and Dragon browser. Both are extras and can be un-installed easily through control panel.