There three best Anti-Virus Software's - 1) Kaspersky (PURE 3.0) 2) McAfee (Total Protection) 3) AVG (Internet Security) along with Malwarebytes Anti-Malware & Malwarebytes Anti-Exploit.
You can choose any one from these three Anti-Virus company that fits your budget and needs.
I strongly recommend using Malwarebytes Anti-Malware along with the anti-virus I suggested to avoid any malware's, spyware's, adware's, rootkits, rouge agents & online protection (It will block malware websites automatically)
Also strongly recommend using Malwarebytes Anti-Exploit. Why? It protects everything else in your computer. From your music, music player, photos, documents, excel files, word files, programs or software's you have in your computer. We all know when you get a virus the first thing it does is try to alter your programs or files & unfortunately if the anti-virus or the protection we have in place is not able to find it. It alters even or photos or image files so it becomes more harder to find the virus or a bug we have in our system. To avoid that & to get good security. I recommend Malwarebytes Anti-Exploit as well.
The system I have is Windows 8.1 Pro which already as Windows defender as the basic anti-virus programs along with it I use Malwarebytes Anti-Malware Premium & Malwarebytes Anti-Exploit Premium.
The Malwarebytes Premium versions costs $24.95 each this for 1 year subscription. This is the best back up or the security you can ever have !!! If you do need any additional assistance. Feel free to ask :) & do let me know if my suggestion have helped you in anyway :) Cheers !!!