I can't decide: Spyware Doctor, Spyware Terminator or Comodo BOClean Anti-Malware, which is the best & why?

I want realtime protection, but I want to make sure it doesn't slow down my PC & is easy to use & understand. And which one provides the most protection, without having to install other programs or toolbars. Or is there another Free AntiSpyware AntiMalware with real time protection that is even better than those? I had Windows Defender, but from reading other Answers I don't hear good things, but maybe those people are wrong...