Fuckin' A.Stock Windows Defender has always worked great for me. I never found a free anti-malware program I liked, but then again I also haven't needed an anti-malware program ever since I started using adblockers. Its really amazing just how much shit that tries to fuck with your computer comes out of ads and badly scripted pages.
Even a relatively cucked adblocker (such as AdBlock Plus) will do a half-decent job of stopping the nastiest shit before the user sees it. A good adblocking solution that's well set up can make it almost impossible to accidentally get malware unless the user does something really retarded like downloading sketchy software and not unchecking all the boxes wrt to bundled crapware. By "good adblocking solution", I mean something like uBlock Origin at browser level or Pi-hole at network level (ideally both, especially if you use your machine away from home).