All antivirus sucks, the only difference is how much you pay for it. You give me an PC with any combination of AV product(s) and 15 minutes and I'll give you an infected box, and it won't just be an Adware / Crapware infection. It will be a Screw you type of Cryptovirus or some serious credential stealing backdoor.
That being said, I use MSE / Windows 8 Defender simply because it's free and the least intrusive of the free AV's and it works great as a canary since every Virus attacks MSE / Defender first and you know you're infected when it keels over, giving you time to do something about it before your Files / Backup gets screwed.
Also, Get Adblock plus for your browser, Disable Non Obtrusive ad's in adblock plus so you don't see the Search Engine virus ads and don't download or install anything from anywhere afterwards.