When I was considering a kindle, my friends recommended one with no backlight as it would be more like a book for my eyes. Any screen with lighting can stop normal sleep patterns and will produce some kind of eye strain.
The downside is that when camping, you need to wear a headtorch to read in bed, whereas with a backlit one, you wouldn't.
However, a normal kindle has served me very well and my eyes don't get tired or sore at all when reading.
Good luck!
------------- The greenest unit of energy is the one that never gets used.
As a poor sleeper, my paperwhite means I can read in bed without disturbing my soundly asleep OH.
Also I can read outside in bright light but OH who uses a normal tablet can't see his screen.
I have had the original basic Kindle, the paperwhite and a Kindle fire they all have their pros and cons.
I have enjoyed the paperwhite for the back light and being able to read at night when OH is asleep. The touch screen however is a pain in the backside and I much preferred the buttons on the original Kindle, it was easier to use.
I like to group my books into collections after I have read them which you can do whit the paperwhite but the touchscreen then becomes difficult as it struggles to differentiate between the sections and which one you are opening.
The HDX fantastic, I love the option of having it set to black paper or cream paper in your book with different coloured text. So much easier on the eyes.
Search function for the internet is fat and easy if you want to look something up. If you like autobiographies then the photos and maps are nicely displayed at a good size unlike on the other two. You also get to see the books cover nicely.
Battery life though is terrible.
If I were replacing mine I would probably just go for the basic with a book light as long as I had my trusty laptop for the photos. No laptop then I would get the HDX.
I can massively recommend a cover from Lente designs though.
I got a kobo instead, so I could download books from the library (bought a basic one). Used it lots in the couple of years I've had it, and not needed to buy a novel yet. Saved myself a fortune.
I have a 10inch tablet and downloaded the Kindle app.
I started reading a book but had some text missing from every page. I couldn't work out why and got very frustrated, then I turned the thing 90 degrees and all the text was there.
Had to start the book again.
I was able to read the book in the dark, if anything, it was a bit too bright.
I haven't yet found out how to turn the brightness down.
------------- I can't add years to my life but I can add life to my years