My son's new laptop had Bit defender installed on it right at the store from the Geek Squad guys. I asked them just about using Windows defender but they recommended the Bit Defender instead.
Either way, Bit Defender was installed for free/was part of the deal so I assume they get a kickback?
I am not a computer guy so I have no idea what is best/necessary as I likely have too much on my PC, which includes the paid Avast Professional home edition, CCleaner (free version) and Super Anti Spyware (paid), plus I am continually clearing my history/data and using CCleaner after I close something out every time I've been into it.
I've been hacked before prior to using these things and not once since but that was quite a few years ago.