For me best tts was ivona-text-to-speech with Carmen voice engine (romanian language)
Ivona is no more availlable for free in google play, now has name Polly and is property of Amazon, so you can install ivona apk fom external source (search in google).
After that you must to search and install desired voice engine apk (Amy for english or search for other).
Availlable here: https://www.ivona.com/us/about-us/voice-portfolio/
Then freeze pico tts, set ivona as default tts and enjoy.