From Microsoft’s 2019 voice report:

• Siri and Google Assistant are tied at 36%
• Alexa at 25%
• Cortana at 19%
• Other at 1%

Another nugget:

In 2018, we found that 23% of respondents currently own a smart speaker with another 30% planning to purchase . In our research in January 2019, we found that 45% of respondents now currently own a smart speaker with an additional 26% planning to purchase one soon.

You can find the report here. It’s an interesting read.