I don't recommend the Sony PRS-500, I do however recommend the PRS-505 (if you can find one since Sony discontinued them). However it's 6" is really too small for PDF viewing and it lacks PDF zooming.

The PRS-600 and PRS-900 aren't terrible by any means. It would be great if you could find one to look at locally to see how it strikes you. There is glare but it's not a mirror like a gloss screen laptop. I didn't suffer much eyestrain as long as I read with good ambient lighting or a book light.