There are a number of choices out there, but one thing is certain, you'll want a combination of products. Personally, I use Avast and MalwareBytes on my machines...have for years. They're both free and do the job well. Others will have their preferences as well, and I'm sure they're just as valid.
i use a free avira antivirus ... it has occasional pop ups but its still free and nevertheless pretty good to use IMHO