A great place to start is looking at some comparison tests:
https://www.av-comparatives.org
I won't recommend anything specific here, but you'll definitely want to look for something with protection beyond just the basics. The big threats these days are ransomware, crypto, etc. and are constantly evolving. Avast Free for example has both Behavior Shield and CyberCapture which are specifically designed to protect your system, even against new or unknown threats. In other words, "AV" is a lot more than just basic AV these days
https://blog.avast.com/the-core-security-components-of-avast-2017
I would also recommend thinking about what other features you might be looking for, and which AV suites fit those needs, while you research which one is best for you.