The problem with antivirus suites is that they tend to change every year. For a couple years one will be decent - then suddenly it will become complete crap. This year it appears both AVG and Avast have gone into the toilet.
Don't use Microsoft Security Essentials - it tests poorly on the independent AV tests.
I have no idea now which AV you should use as my usual recommendations appear to have become crap. As usual, the software industry is a disaster and very few pieces of software are either functional or reliable.
If you really want to avoid malware, switch to Linux and Stop Clicking on Sh*t.