I use MSE on 2 of the 3 desktops at home, the other runs nothing as its linux and I don't care about it. MSE is free and much less intrusive than other AV software. The others are all heavier on disc I/O which irritates me and wastes I/O read/writes on my SSD raid! I would not rule out using Avast, a couple of colleague's use it and are happy with it.. most Dev's I know wont use any, they say it takes the fun out of using the interwebs
I occasionally run M'bam when I think I have clicked on something dodgy or a link Steve or Ian sent me
Viruses are much less of a problem these days in comparison to malware/crappy security flaws in SSL certificates?