Ok, I'm inspired to post this review. :)
Avira is the best anti-virus right now if you're looking for a free solution. It has one of the best virus detection rates and the lowest impact on system performance (better than Windows Defender / MSE) you'll find at $0,00. Also, it only displays 1 pop-up recommending the paid version when you start the computer and that's it, not countless annoying ads like Avast has been displaying recently.
It's a trustworthy company, not those silly and disrespectful (mostly Chinese or partnering with them) companies that spread ads and install bundles like they're malware themselves (hello Baidu).
I recommend it to everyone!