Alexa will win the smart assistant war because of first mover advantage.
eBay won the online auction war because it got susbtantial traction first. Why go to any other auction site if eBay has substantially more items for sale?
Alexa will kinda win in the same way. Because it has the most users, Alexa has more data, which means the machine learning will be learning more, and quicker.
People will notice that Alexa is more natural and understanding than the competing devices, and gravitate towards it. There will certainly be smart assistant envy.
That is only half the story, because interoperability is also important. If you use Google Calendar, then using Google’s device makes sense. If you use Skype, then Cortana could be your choice.
So far Alexa is doing well – it can access calendars from its competitors. And Alexa can directly call mobiles and landline numbers in North America, as well as Alexa-to-Alexa calls.
As long as Alexa provides the features and interoperability that people want, Amazon will be unstoppable. They will become the new Android. And perhaps the new Google.