Voicery and Storyline are the two that connect with my interests.
I think Voicery does itself a disservice by featuring a "pick the human voice versus pick our machine voice" demo quiz on their website. I got 100%, and it led me to emotionally response "they have failed", but in fact the voice sounded great.
A more useful demo would have been to hear a range of different voices and be able to put my own text in and hear it read back.
But it is not the point that a machine voice can be determined versus a human voice. The important question is "does the machine voice sound good enough".
Instead, their marketing approach has forced me to make a comparison in which my conclusion was that they tech "lost" in some sort of contest.