Something that comes up often is what antivirus software to install . It is hard to get a good comparison as many reviews are done with publishers who gather advertising revenue however this one highlights that if you practice good techniques Windows defender will do the job. If you have a slow computer removing one of the commercial antivirus programs and enabling windows defender could speed up your machine.
Be aware that if your subscription for a commercial one runs out most likely your protection will stop at that point also. Many new computers come pre installed with a limited subscription so keep this in mind. Personally I use Windows defender.