I hate the stream voice so much, that I take my bookshare books, open them 
in k1000, and save them with the voice I like, as mp3 files.  Then I play 
them on the player.  I absolutely love my milestone 312, but I don't think 
the synthesizer is much better than the stream is.  I think most of the book 
reader devices, try to sound like voice-over, which is awful if you read at 
any speed, because it mumbles.

Synthesized voice choices are as personal as anything, one is beloved by one 
person and hated by another.  Personally, the old doubletalk speech is the 
best.  That's for me, and people here will insist I am as crazy as a loon.
Get voice samples of the TTS engines, or do what I do, and convert text to 
mp3 and play that.