Edge lists a lot of voices. The ones with Online (Natural) in their name sound the most like a real person. They're made on Microsoft's computers, not yours, so they only work while you're connected to the internet.
The other voices are the ones installed on your computer. They work without the internet, but they sound flatter and more robotic. If you lose your connection, switch to one of those.
Too fast or too slow? The speed slider is in Voice options too.