I haven't seen the Update bug on KFA, it's always up-to-date every day automatically on my mate laptop. KCS though, does have major bugs on Windows 10 at the moment, I won't recommend it until it's Stable.
Big Defender is extremely problematic on Windows 10, and heavy on the resources.
Avast has nothing against the other two besides the hardened mode, it has a shady privacy policy on top!
Windows Defender is a resource hog compared to Third-Party AVs, not to mention most of the options for it can only be tweaked and enabled through group policy and regedit.