It looks like Google will allow app integration with the Google Assistant: https://developers.google.com/actions/

Here's Tim O'Reilly making the case that Alexa is in a different class (from a UX perspective) than Google or Apple's AI assistants:

https://www.linkedin.com/pulse/what-would-alexa-do-tim-o-rei...

I think the point about Alexa's great interactivity coming from having to build for a device with no screen is a strong one. Though I think that the best AI-driven UIs in the future will have to bridge the gap and be able to display content usefully on a screen (or many screens), while also preserving that concept of knowing what the current context is (i.e. "skip" means "skip the track" if I have music playing, but might refer to a different app if I have youtube running).

I agree, I don't know if it's the best. I just know that it recognizes the words I say to it better than any other I have used, oftentimes without needing to speak in the artificially clear voice that most tend to associate with voice control.