Avast is free. and comodo offers a fully fledged security suite all for free. there's not even a paid version of it. it's comodo internet security, it's extremely hard to bypass, and i recommend you use it. i've never been infected ever since i switched to it. it even monitors your registry. but if you want just an antivirus, i suggest avast, or avira. for anti malware, malwarebytes works great. Also iobit steals from the mbam corporation. :6
AVG is free though.
EVERY OTHER ONE Costs money. Norton you can only use for a limited time and you have to re-pay a **** ton of times.
Registry mechanic? **** no. That will GIVE you viruses.
If you want something good, I suggest something from Iobit. They cost , but its a 1 time cost and it's the only thing you need. (Advanced System Care)
Finds viruses like a hawk.
And other things.
Oh wait, am I derailing here? ****.
No, Windows Defender is best. [It never catches viruses so you think you don't have any!! Awesome.]