I use Avast (free version) on a number of PCs, and standard Windows Defender / Security Essentials on others. Avast is guilty of “feature creep”, as they keep adding more and more crap (overhead) to the program, in many instances duplicating features that exist in CCleaner. As I move PC’s over to Win10, I’m just letting the built-in Microsoft stuff do its thing, and then run the occasional sweep with Malwarebytes and CCleaner.
I use a combination of Avast, Malwarebytes and CC Cleaner on my Win 10 laptop. These are free versions, and they are light on resources compared to NAV. No problems.