Google voice typing is a Docs feature, not a system feature
This is the whole comparison in one sentence, so it is worth being exact. In Google Docs, Tools › Voice typing gives you a microphone button, and it works well: dictate paragraphs, say “comma”, say “new line”, tell it to bold a phrase or move to the end of the document. It is free and there is nothing to install.
But it lives inside the document, in Chrome. Switch to Slack and there is no microphone button. Open Outlook and there is nothing. Move to a Jira ticket, a terminal, a Figma comment or a form in Safari and the feature does not exist. Android's Gboard covers phone typing, which is a different device and a different situation.
So the question is not which recognises speech better. It is what proportion of your writing happens in a Google document. If the answer is “nearly all of it”, Google's option is free and you should use it.