There isn't the best one! A lot would depending on how ofter the antivirus is being updated! So far I found that Avast is pretty good, Panda is decent, Norton was good about 15 years ago, but not anymore, Kaspersky is decent but slows down the PC and has a lot of bugs, McAfee is the most overrated for sure - stay away from it, DrWeb is unknown for many but is pretty good for the price, some people say that AVG is good, but personally favour Avast to AVG, after AVG failed to spot 2 trojans and Avast found them. It's your choice, but remember that a free version is not as good as paid one, especially if you browse a lot or download a lot of files.