I have been in the IT Industry for around 15 years and the best way to put it is "you get what you pay for".
AVG and MS Essentials are complete rubbish. Nortons is ok but not really the best as it monopolizes your computers resourses.
I have have over the years use a combination of Kaspersky and Spybot. Both are very good and will usually pick up issues that AVG or MS essentials dont or cant detect. I have recently heard good things about NOD32 but I have not had the opportunity to test it for myself yet.
http://www.av-comparatives.org/ is worth looking at
and so is http://www.bestantivirusguide.com/best-antivirus-comparison-chart