TTSynth.com alternatives

I'm currently using this API in my mobile app and I really like the results and the features. Pricing seems fair; however, I have had some issues with reliability. While it works most of the time, their platform seems to go down more often than I would like and there is often little to no communication from the company. None-the-less, I will continue to use it as their huge library of languages and voices really puts them ahead of other such services.