I've tried a lot of them, and the best I found so far is Edge browsers built in microsoft (natural) voices, which I call via javascript or the browsers read aloud function.

Checkout https://github.com/rany2/edge-tts , which exposes it as a Python library and a CLI tool.

I’ve been enjoying Kokoro

Amazing what it can do with only 82M parameters

https://www.kokorotts.io/

Curious your use case, I now have quite a lot of experience with releasing desktop apps, and I have done some accessibility work as well, and may be curious to put together a TTS toolkit as well into a desktop app (or even Handy)

piper's amy voice is pleasant enough to me for reading articles, and it's instantaneous and trivial to use, just download the binary and model file.

Wow, this is much faster and higher quality than the meloTTS program I was using before, and has many more voices available... although it doesn't appear to support Japanese.

Thank you!

I've used Speech Note, which works well for STT and TTS.

Been having fun with this one

https://addons.mozilla.org/en-CA/firefox/addon/read-aloud/

Read Aloud allows you to select from a variety of text-to-speech voices, including those provided natively by the browser, as well as by text-to-speech cloud service providers such as Google Wavenet, Amazon Polly, IBM Watson, and Microsoft. Some of the cloud-based voices may require additional in-app purchase to enable.

...

the shortcut keys ALT-P, ALT-O, ALT-Comma, and ALT-Period can be used to Play/Pause, Stop, Rewind, and Forward, respectively.