The TTS voices are rather speculative (each person has their own preference). I might like Cepstral's Emily where John might prefer the L&H British Female voice. A matter of personal choice for the gender of one's Hal.
Dragon Naturally Speaking 7 seems to be a favorite among several users then again some use the one that came with XP just fine. IBM Via Voice also works well for a lot of folks. Again...personal preference.
Some questions just don't have one right answer. LOL!