I was a big Cortana + Windows Phone fan (big enough even that I had one in use in 2014) and it did start out competitive. Over time though, Siri got better, Alexa got better; Cortana never did. Microsoft shows an inspirational video at Build every year, but what they show never seems to become reality.

In contrast, I started investing in Alexa mid/late-2018 and while it was great to start, it has become increasingly useful. It makes phone calls to businesses, and gets it right very consistently; it knows business hours; the automation has become more powerful over time (a category Cortana never even began to touch); and the integration ecosystem is superb.

Alexa keep improving, too. Yesterday I invoked a routine that included playing music, while the invoked service was busy playing on another device. While in the past the music just wouldn't have played, now she says, 'Amazon Music is already in use on another device. Did you want to play Thunderstorm Sounds on Bedroom Sonos?' That's just one example, but they are numerous and regular enough that I was able to pick one from just yesterday.