I have all of those except Peter, and instead of telling you which one is best, even though I ticked off Heather in the poll :D. It might be better to tell you how they work out for me.
Out of the three I own, Heather and Ryan sound the most natural and they come with their own editor, whereas Jennifer sounds nasal and does not come with any way to edit her voice outside of TA.
The downside to Heather and Ryan is that they don't respond to regex very well and will skip words that are entered as an expression in the basic editor – sometimes they’ll simply skip a word if they don’t like it, and you’ll have to play around with it until you find out where the fuss is. They also can’t be utilised by the system or any program other than TA. With that aside though, I find Heather's voice very soothing, and Ryan's somewhat on the gruff side – but in a good way. He has what I like to call a "whiskey voice," and the tone he speaks in is very close to natural. If you’re looking for a nice read for long periods of time, I highly recommend either of these two.
As for Jennifer, I’d have to say that the downside to her is that she doesn’t sound as natural as Heather and Ryan for long reads. She’s very nasal, very flat, and almost robotic, to listen to. But on the upside, she’s very dynamic, responds well to regex and regular edits in the Basic editor and she can be used with the system and any other program that is willing to utilise her.
In all honesty though, and I know you didn’t mention the following: But in case you haven’t considered them, or don’t already own them, I’d say that out of the RealSpeak females, Jill is a step up from Jennifer, and Samantha sounds far more natural than both for long reads, even though she’s a little comical when it comes to question marks, and they all follow the same method of usage as far as program compatibility and regex goes. I quite like these voices for their diversity, since TA isn’t the only program I use.