Glare vs e-ink. This is well known and understood. Focusing through a layer of glass is one thing, but the bright/contrast, and the potential glare from the background makes the eyes work harder. Keep in mind that for a reader, many users may be looking at it for hours at a time. I know because I am one of those people that has problems with eye strain.
Anyway, you can google the topic yourself and you will see why. Of course you should get what you like. When the problem becomes real you will know.
Here's one from ZDnet
It's long but the verdict is "The iPad appears to be adequate for light daytime indoor reading, but fails miserably as an outdoor reading device"
this is a long-running debate that i don't think will be settled based on the opinion of zdnet. the poster asked because the medical community has not reached a consensus.
i prefer the kindle for long reading sessions. but, the ipad isn't so bad, especially if you are reading in a well-lit area for less than three or four hours at a stretch. i have never found glare to be in issue with the ipad. of course, this is my personal experience.
the consensus among users: some people have issues with the glare. others don't. get what you want.