Avast. Less false positives.
assuming you don't use a pirated version of windows, MSE.
Microsoft Security Essentials here too, never had a problem with it, most of the time, i forget its there, exactly what I want from my AV.
Microsoft Security Essentials here as well. Why? I have never seen it ask me to pay for a subscription.
"My sword? [Heck] yeah I know how to use it. What's to understand about swish-swish-stab? It's a [freak'n] sword dude, it's not a fighter jet." -Tucker "This One Goes to Eleven
I used Microsoft Security Essentials for several years, but lately it seems to be lacking...
Switched to AVG Free a few months ago on both my PCs and client PCs and have no regrets. It is extremely light-weight and it detects and removes things neither MSE or Malwarebytes did. It also recently updated to the 2013 edition which is even better.
I've never had a problem with AVG. Been using it for about 2 years now, updating it whenever possible.
another vote for MSE (Microsoft security essentials).
My vote goes for Microsoft Security Essentials (MSE). I used to like Avast, but they added a lot of ads of their paid version recently, so I tried MSE and I liked it a lot. It does not have all the features of Avast, but it's light, fast and has no ads
MSE and Malwarebytes
Would also include CCleaner even though it's not an anti-virus or anti-malware software. It keeps your system clean.
Microsoft Security Essentials for free. It's also pretty much built right into Windows 8.
ESET NOD32 when you pay. That's from my personal experience.
I'm kind of torn between Avast and AVG. I like them both, but I've used AVG for longer. Avast is probably the slightly better of the two.
I also use SpywareBlaster and Spybot Search & Destroy as secondary protection.