as long as you have a clean system to begin with, Windows Defender will keep you safe. I run it along with Spybot Search & Destroy. Never had an issue.
I've tried a heap of Anti-spyware progs and am dissatisfied with false alarms, annoying pop-ups/alerts. i like to set and forget. NOD32, Windows Defender and Spybot suit me perfectly. Just ensure to update Spybot at least once a week