The answer depends on where you ask your question.
There are people here who will give their honest and unbiased assessment notwithstanding this being the Avast forum.
There really are enough sources for you to make your own decision, AV-Comparatives for example.
Whilst MS defender has improved its detection rate it doesn't cover as many areas as Avast does, even the free version.
Plus (AV-Comparatives) don't test all areas of Avasts protection.
MS defender also has a high number of False Positives in the AV-Comparatives tests, which can happen when trying to improve detections.
That said there is only one person who can make that decision for 'you' and that has to be based on your investigations and your requirements.
Avast Free suits my needs and I have been using it without infection for over 16 years, so I guess you know where my answer lies.