I honestly wouldn't trust any of these free bits and pieces that you've never heard of before. In my experience, they
nearly always fail to do their job properly.
I reccomment Microsoft Security Essentials (MSE). It's bundled into Windows 8/8.1, so you don't need to install it if you're on anything above Windows 7. If you're on Windows 7 or below, you can download it
here. It's free, lightweight and does its job very well.
I also recommend running a
MalwareBytes scan once a month, which can also be downloaded for free. It'll pick up anything that MSE misses as no anti-virus software out there is 100% perfect.
If you're hell-bent on spending money on anti-virus, your best bet is
AVG.
(Also works in IT if that adds any kind of 'stamp of approval')