I must admit that I'm pretty much done with text to speech converters to be honest. I've tried all of the above and then run the output through a couple of different vocoders, some free, some paid for. Result has been, in a word, awful and I am now of the opinion that I need to create the speech with my own voice instead. Not an inspiring prospect, which is probably why I have done that yet, but it has to be better than the current run of text to speech converters currently available.
My vocoder of choice is now Vocodex by Image Line.