Well, if you want to buy a good antivirus with anti-ransomware support, you can choose from these.
If you just want a simple antivirus that will just do the job, you can use Avast, AVG, Norton, Nod32.
Also, it is very important. Purchase Windows 10 if you are still on Windows 7 or 8. Windows 10 has many security updates and you won’t get a virus that easy.