The one that I felt is the best is avg anti virus. It's light and it's somewhat free. But nowadays, virus attacks seem to be less relevant as i guess hackers don't really target small time pc users nowadays. More effort I guess is being diverted into building technologies that are involved in block chain technology.
I have used other anti virus and some are really heavy on the system and lags the whole pc into use frustration. The other thing you can use to improve the pc security is to install malwarebytes. Quite good to detect Mal wares. Once in a while it is really important to get your pc scanned. There was this time that I experienced such an extreme drop in my Mac books battery life that I later discovered was the work of tons of virus that were on the computer.
I downloaded avg and updated the database and scanned the system. Removed all those unwanted parasitic virus and used malwarebytes to scan for Mal wares. After clearing out all of those stuff, my Mac books battery life improved and was back.
Do scan any pendrive that you put into the pc and maybe get a browser that extends the virus capabilities. Most virus enter into the computer from browsers. Usually if any deadly virus comes into your pc and something has been affected. Just Google it to find the solutions.
Usually there are plenty of solutions out there. Nowadays virus doesn't really harm out computers anymore.