If you’re just looking for basic cybersecurity protection, then yes, Windows Defender is fine. But if you have a lot of sensitive information on your device which might attract hackers — banking info, login details, private files — then no, it’s not “enough”. For example, some ransomware like cerber ransomware that targets to destroy your data and demands a cryptocoin payment cannot be detected by Windows Defender.
If you want to try AVG free on your computer, you might want to disable Windows Defender first. It is not recommended to run more than one anti-malware program on a computer at the same time. It could slow down your device and cause some performance problems like frozen screen due to incompatibilities.