Used to use AVG a few years ago, but didn't seem to be keeping all the riffraff out the last couple years. Been using Avast for about a year, working great and I just set it to never show me any notification unless something is going wrong, which has been almost never. Every once in awhile I wonder if it's even still there, but I open the main program and it's working well behind the scenes.
Once I get an excuse to, I'll probably switch over to try Microsoft's, because I like to keep things consistent.