I have an Echo dot - and from the article I can tell the winning difference will be the amount of devices controllable - with Amazon way ahead of Google. I can control a Nest as well as lights. With Amazon's market share, it's their market to lose, not Google's.
I don't know how many 'things' Google's can do compared to Amazon's (like ordering, calling, etc.), but it will be the commonplace things that will win the day for the eventual champion (if there is only one - I suspect they will both maintain some marketshare and Siri will only be in Apple-centric households, and MS will fade away).
It will be an interesting competition to watch!