Well, for starters, you shouldn't ever have more than one 'Anti-virus' program installed at once. AVG and Avast will cancel eachother out with their realtime protection. I've been using Avast! for years, and have never had a single virus on my PC with it.
Avast + AVG = bad
Avast + MBAM = Perfect
AVG + MBAM = Perfect
MSE + MBAM = Sufficient.