Google TTS supports both. Maps prefers the cloud one so that you're not at the mercy of whatever TTS your manufacturer has installed (Samsung uses their own, ri

Google TTS supports both. Maps prefers the cloud one so that you're not at the mercy of whatever TTS your manufacturer has installed (Samsung uses their own, right?), but will fall back to the local one it there's no connectivity. I can't remember if the Google TTS implements that or if it's custom to Maps.