Well, a lot of interesting personal opinions and a perhaps a hint of prejudice.
In all the time I have used it avast has never found a virus on my system (even though I have planted some real viruses on my system in my mail folders). avast has reported a number of false positives on my system.
The Microsoft malicious malware tool has reported neither real viruses nor false positives. In that sense it has caused me less trouble than avast. I have tons of bandwidth to download it, tons of CPU capacity, about half a terabyte of disk space ... and nothing against it.
We all have to make our own choices.
If I may be permitted a word of criticism of advice posted in this thread:
I feel that Microsoft "Update" is a waste of time .
... is one of the most unwise recommendations to average systems users I have ever seen in this forum.