Hi, i dont like to use antivirus software because my computer is crap. Then i dont want a antivirus software. I want like ThreatFire but only for scan for downloads and sometimes scan the computer like "Quick Scan".
As "experty" as @MalwareFire is I would reccommend some real-time protection, perhaps MSE/Windows Defender?I would use Malwarebytes free in order to do that. A threat scan can take up to 30 mins to run, depending on your computer specs and it covers 99% of the location where malware usually hides.
If the OP wants real light-weight and efficient protection, I would go with Panda Cloud instead of MSE. And Windows Defender is more of an Antimalware rather than an Antivirus, but it depends of what he really wants in the end.