The fastest to output text would be to paste it, which can be done using the "Set a Text Value to the Windows Clipboard" action and a keypress action that presses Ctrl-V (or Shift-Insert)
For literal typing, the "Quick Input" action can send keypresses quite rapidly, however there is an issue with the more recent versions of Windows 10 (2004 and onward, as far as I'm aware, though it doesn't happen on all machines) where Windows executes the keypresses less quickly, despite VoiceAttack issuing the exact same API calls as before.
You can try experimenting with the "Resource balance offset" option that can be found under the "Advanced" button on the "Edit a Command" window (as it is an advanced/experimental feature).
Even enabling that option with its default value of 1 yields a slight speed increase, and higher values even more so, though this does come at the cost of higher CPU load while the keypresses are processed.
Note that the option applies to all actions within a command, so be especially careful if you're using any loop actions and/or have the command set up to repeat itself.