My personal opinion is not to trust security to a free service - they'll do fine for most things, of course, but they're usually not as thorough. Personally, I'm a fan of Bitdefender......I don't know if it's the best, of course. I don't know if there is a "best".

Of course they're trying to sell you things - their advertising is the price you're paying for their service.

Malwarebytes

PCMag is an independent, trusted source that has been in existence for over 30 years. Its ratings are based on tests done by itself and independent testing labs. Links to its most recent ratings are below. On its site you can also find articles about how the testing is done.

I've been using Norton for nearly 10 years - I used to get it for free from my ISP, that stopped and I pay for it now. I haven't had a single incident in all that time. The cost is nominal, something at or around $15 per PC per year for a site license.

The best security/anti-virus protection is provided by a careful user who doesn't click on links on sketchy webpages and never clicks on links that arrive from unknown or questionable sources. And users who travel around the internet carefully. These protection measures are quite reliable and are nearly 100% effective

Ratings of free antivirus software

Best Not Free Antivirus software

If you know how you got the virus and what to do to avoid getting infected again, that will be a better benefit than just choosing a different antivirus. If you do not know how you got the virus or are not going to change your computing habits, then it really won't matter which antivirus you use because you will get infected again. It's only a matter of time.

Windows 10 comes with an antivirus built in. It is somewhat better than a free one. Malwarebytes is excellent and there is a free version. Anti-virus and anti-malware are not the same thing exactly. Even the most careful user can get caught with a virus or worm. A trusted friend could have it attached to their email. Make sure your incoming mail is being scanned.

I personally wouldn't use or rely on Microsoft's offering. It's been a middle of the pack performer over the years, with many better choices to use. Testing and ranking reports have improved but there are still better choices.

I use both the antivirus in Windows 10 and Malwarebytes. For many years I used the free Malwarebytes, but now pay for it by personal choice. I have used Avast and did not like it at all. Also have used Nortion and McAfee and hated both of them. Highly recommend Malwarebytes.

I have McAfee on my laptop because that's what came with it, and I don't hate it. From time to time it offers to remove internet tracking, but the last time it did this, I had to log back into a few web sites, but not all. It did not affect my email log-ins, but I think it did force me to log into Houzz again.

I have Kaspersky on my L.A. desktop, and it allows me two more devices, and so I added my phone and tablet. I might want to switch my laptop to Kaspersky when McAfee subscription expires.

I had Avast (free) on a laptop before and did not really like it. One of the things I've experienced from free virus protection is that a lot of the updates had to be done manually, but they may have improved that by now.

I would rather pay a nominal fee and have something that works seamlessly. But if you only need to protect one computer and do not use it that often, then a free protection might be better for you.