I'm the Official Unofficial Tech Support Wienie for the family so they get free support in exchange for me playing around with various AV programs. By no means am I an expert. I've tried AVG, Avira, Avast, and MSE, and have used Malwarebytes to clean up stuff when people weren't careful (I'm talking to YOU, Dad).
I gave up on AVG about a year or so back. The version at the time was giving significant problems across multiple machines so I went to Avast. Avast worked but it required a bit more hands-on and my "end-users" were bugging me with questions when they'd get warnings and the like. Then I tried Avira but it didn't play nice with a couple pieces of software, though for the life of me I can't remember what the specific problems were. On most of the machines, including my new laptop, I'm now running MSE. So far, so good. I think we still have Avira running on the kitchen PC and it hasn't coughed up any software incompatibilities in a long time, nor has it let anything slip through.
All of them worked for the most part (though AVG did have problems with a couple versions), some were a bit more intrusive than the others, and a couple of them did let slip by a few problems, mostly Day Zero-type stuff where the definitions didn't catch up with my family's ability to hang out on websites where this crap is found. And none of them can do anything about Dad installing 6 different weather widgets (including frickin' Weatherbug after I told him specifically NOT to install that one) and over a dozen toolbars.
They're probably all just fine for a knowledgeable PC user. For installing on the family and friend PCs that you have to babysit, my amateur-IT picks are MSE and Avira.