The best thing to do with the highest ROI is your own projects for a portfolio, ideally things which haven't been done before (e.g. in the context of data science/ML, not the Titanic dataset or sentiment analysis of Trump's tweets).
Everyone has their own learning style, but I stopped doing MOOCs once I realized that doing work in a similar domain is more practical.
Thanks for your response. I agree that portfolio projects show more about a person than their certifications. I never liked taking exams in school anyways. :p
Regardless, do you think that there are any MOOCs/certifications that are worth investing in, if you were going to get one anyways? Say, if your employer is paying you to get one, etc.
Everyone has their own learning style, but I stopped doing MOOCs once I realized that doing work in a similar domain is more practical.