Welcome

Very astute question. Best is in the eye of the beholder. For me and many at this forum, we believe that MSE is best
Best because it uses very little resources
Best because it is the only AV made specifically for Windows by the creators of Windows
Best because it has a very good track record of stopping Virus and Malware.

I think its best because, in addition to the above, it is the only AV that I have seen at this forum that has not caused computer problems, such as freezing, BSODs as well as other problems

This list can be useful:

Probably the Best Free Security List in the World

Don't just look at the editor's picks. Often in the comments section you can find out about a software you are not familiar with. Myself, I prefer scanners. To run with real-time protection is like taking a shower with a rain coat on. On occasion I'll run a browser in Sandboxie if I have no confidence in the site or it's a link I'm not sure about. There are other browser shields too, probably in the lists in the link.

Also I believe some like to run a VM just to run a browser to risky sites. Many ways to skin the cat. It's been my experience that "real time shields" often create more problems than they solve.

Just my $.02