Read the specs on the box or online description. I've always used the free versions, but I don't go to a lot of sites some folks do either. If you read the specs, you'll see a lot of "features" listed that vary from product to product. Which one is best? Ask 2 people and you'll get 3 or 4 answers! I've read a lot of reviews over the years, and no two report the same thing. I used the free Defender in Windows 10 in the insider pre-release days, and am using the free AVG on 28 computers I support, and almost never have problems. YMMV.