Welcome OP Amnesia to MT...
Paid AV's usually include a lot of extras that you may not need, such as software updaters, registry scanners, update tools and such. Personally I see no need for extra components beyond the AV/Security and scanning capabilities of any AV. Free AV's often use the same core components as their paid-for counterparts and the free ones often score just as well as paid versions in the various AV tests found online. I don't put much faith in the tests myself, I go by how well the program works for me on whatever computer I use it on, and also rely on the details I find here on MT.
Windows Defender/Antivirus works well for a lot of people. It is built in to Windows and is free to use, no nags and no questions asked. WD's performance can be improved with Andy Ful's ConfigureDefender tool and there is another MT member here,
@danb, he is working on a very impressive alternate GUI for Defender. Earlier this year I tried a few different AV's, but in the end I settled back with WD and ConfigureDefender set on High. On my personal computer that combo works fine. It even saved me a few days ago, when I clicked a link in a Google search when I was having trouble with Groove Music. WD alerted me and blocked a potential trojan.
My other opinion is mostly personal preference but I find WD to be kind of high maintenance. In my mind I don't think I should need extra third party tools to make the AV work better, the AV should do the entire job on its own. On the laptop I use for work, WD seems to have a problem with Windows updates. Whenever there is an update that is trying to download or run, WD loses its mind, its RAM usage goes up and it throttles my hard drive for a while and the computer slows down to a crawl. The surface of the laptop will get hot too, not too bad but definitely warmer than usual. WD will settle back down once the update is completed or paused. I had this exact problem just this morning, and it was not fun to have to sort that out on a Monday morning.
I have had more than a few compatibility problems like that with WD. As a test, I installed the free version of AVG on my work computer today. So far it is working fine, laptop is running cool and even though I know RAM usage is not a very relevant benchmark of an AV's performance, AVG Free is using about the same or a little less RAM than WD did. I added the AVG browser extension and turned off the Performance scan to help keep the upgrade offers down to a minimum but other than that have made no changes to the settings.
No matter what AV is used, no AV will catch everything and nothing can take the place of common sense and using good online hygiene, knowing what to look out for and what to avoid online. If it were not for the strange conflicts I have had between WD and the Windows updates I would still be using WD on my work laptop. As it is I can not afford to have delays in my work day because of technical problems, so I am trying AVG for now. That is my sole reason for changing AV's and I will change again if I need to. AV choice is just a matter of personal preference, you can read reviews, try a few and use the one that works best for you.
Sermon is over now.
C.H.