What advantages does Defender have ?
It’s built-in, it won’t harass you with pop-ups and requests for money, and is lighter than some competing antivirus solutions. It won’t attempt to harvest your browsing data and make money from it, as some free antivirus programs have started doing in an attempt to make a profit.
Windows 10 for example also includes various other protections introduced in Windows 8, like the SmartScreen filter that prevents you from downloading and running malware. Chrome and Firefox also include Google’s Safe Browsing, which blocks many malware downloads.
Defender is also by far the least intrusive, considering most other antivirus programs come bundled with crapware, install problematic browser extensions, and contain occasional popup ads, this alone is where other Av programs can ruin your PC by secretly installing rubbish you think you need or didn't realize was installed, Defender works with Windows so it knows not to install rubbish without you knowing.. source
http://www.top10antiviruslist.com/