I also like Microsoft Essentials. Low on resources and it does the job at keeping me up to date with definitions. I had Norton 2010 for about 5 months and it stopped working and caused me many errors. I even contacted them and they couldn't even fix it. That's when I said Goodbye Norton 2010. It was a waste of money if you ask me.
So far Microsoft Essentials has been a savor and it's free.