Posting from Geoff Simmons at:
I have personally used a number of different engines and voices. I evaluate a voice by the following characteristics:
- Meter - Is the pace of speaking consistent with what you would expect?
- Variance - Does the voice account for any difference based on the inflection of the word in context? This is generally pretty hard to do, so voices that excel here get a few bonus points, but it can be taken too far (see below).
[Update: The total for IVONA is now correct. Thanks for reporting that.]
Classic Text To Speech Engine ($2.99 - ~10-20MB/voice)
Quality: 7 Meter: 8 Variance: 7 Playability: 10 Total: 32
Covers the most languages of any engine (40+). They also have a few different voices for English. Victoria is my favorite. She has great meter and enough variance to keep it non-robotic. The sonic quality is decent, but not the best. One thing we noticed while working with SVOX voices is that it is actually very hard to switch between different variants for a particular language-country combo. iHear Network has deeply integrated with SVOX to provide the best TTS experience. SVOX users listened to over twice as many articles as IVONA users, and over 10 times as many compared to most other engines.
*NOTE* CereProc doesn't have enough users to have a very meaningful Playability score, but I would expect it to be in the 8-10 range, which would put its total up to the 34-36 range.
ESpeak (Not one of the top 7)
Quality: 2 Meter: 3 Variance: 1 Playability: N/A Total: 6
This is possibly the worst voice I've ever heard. Switching between variants has always been a problem with Android's TTS API, but I know a lot of tricks to get it to work, and even I had problems with this engine. ESpeak sounds worse than old school Stephen Hawking. I tried to download EasyTts, which supposedly is an upgrade of ESpeak, but it just sounded like Pico US.
In summary, it's really hard to beat Ivona, considering that it is currently free, unless you don't want to download the 250+ MB data packages. CereProc voices seem to be the best value for the money of all the pay voices, and it will be very interesting to see if they can catch up with SVOX in popularity. Considering that you get as good or better experience for almost half the price, I can't see why not. I look forward to the day when all android devices come with a nice premium voice as a default, but until then, there are some good options available on Google Play.
Don't forget to check out iHear Network for a great Social News Narrator that reads Twitter, Facebook, and Pocket to you out loud.