i personally use a combination of windows defender and malwarebytes free edition. i wouldnt suggest using windows defender as your only anti virus solution.
malwarebytes does a great job and you can let windows defender run in the background and only scan using malwarebytes for occasional scans when you feel like.
I used to use the free version of Bitdefender, but their root certificate kept producing issues when trying to browse the Internet after a while. Might try it some day again, especially if I buy the paid version, but for now I will stick with Kaspersky. Kaspersky Free is pretty good, though occasionally there can be some notifications that are a bit annoying. Another option I might try is Malwarebytes, mentioned by the user above you.
I see nothing wrong with using windows defender. That is what I use on my windows computers. In addition I have malwarebyts installed as a companion utility. Never had a problem with it. I have tried just about all of the free ones over the years and a couple of the retail ones.