As long as you are smart about how you operate on the web, then Defender is good enough. If you are downloading programs from strange websites or clicking links from unknown emails, then it wont be enough. I have found most security software does more harm than good by blocking good programs and slowing down your system.
I do like malwarebytes. I run windows defender and the free version of malwarebytes. I run a scan on malwarebytes every so often as it can find malware that defender may not be able to see and it not intrusive on your system.