Google ones seem best, but I worry that the price could be driven up by a few users maliciously trying to drive up the price. Not sure if there is a way to cap per user. Or if that is even a good approach.
I wouldnt mind integrating speech to text in my game, and therefore may be interested in writing the necessary playmaker actions to bridge the asset and playmaker. But definablely, choosing the right asset would be key.
(I am not using mobile device, but a desktop and htc vive).