I would argue that they are as bad as each other. I have to repeat most voice commands to Siri and Alexa than getting it right first time. No experience with Google.
Voice assistants were going to be this revolutionary new category. I think Amazon was going to populate a whole office tower in Boston with Alexa engineers at one point. There have been incremental improvements here and there but, to a first approximation, none of it has really worked out.