In free Antivirus Avast and Bitdefender's free versions are best in my opinion and in paid ones Eset and Kaspersky are good. But to be honest if your machine's resources are low then I'd not recommend you to use any antivirus except Windows defender, because all of the third party ones will make your PC slower. Here are good collection http://www.pingzic.com/best-antivirus-programs-for-windows-10-free-and-paid/ of antivirus software and the author has categorized them in Free and Paid ones. Moreover, the author has also mentioned about some Antimalware executable service error that makes PC slower and it occurs because of Windows defender tool, if you face it then also not use the Windows defender and just turn off Windows defender. I hope my reply would help you, if you need anything else, just reply to my answer, I'll reply you soon. Adding links below so you can find the free ones easily, for paid ones just search them on google.

Avast Free: https://www.avast.com/free-antivirus-download
Bitdefender Free: http://www.bitdefender.com/solutions/free.html