The TTS performance graph is interesting but it would be even better to add another dimension for comparing their resource consumption (code size, RAM, CPU usage/speed). For example, if "Windows Male" is https://en.wikipedia.org/wiki/Microsoft_text-to-speech_voice... then it's an offline-only synthesiser that is relatively small and fast, while the Google ones are probably massive neural models that are only available as a service. Yet their speech performance seems to be quite similar according to that chart.