I can read on either with absolutely no problem... I'd like to have a backlit device for night time reading. The previous backlit devices I've read on are my PDA (Palm Zire72) and my iPod Touch. I'd like a 6-7" backlit reader..
I think our eyes are as individual as we are.. My eyes can't see in bright light (the lights from a car coming towards me), but I know many people, who's not bothered at all by it.
I don't think a discussion which is best for the eyes will go anywhere.