We have used the Kindle apps on phones (Droid Maxx) and lap top, as well as the Kindle Fire. I just wanted something to read a book on outside. My folks have a Nook and its the same can't seen the screen issue in daylight. The Kindle paper white was the easiest for me to read outside in the daylight as well as at night. Its not overly large and being able to adjust font size was a big help (eyes just don't work like they use too
). When our Kindle fire died (bad charging connection) we bought a Kindle Fire HD but it won't run Java and so some websites we liked for the GB would not run. So we returned the Fire HD for a 2nd paper white and now we can both sit outside and read. Local computer shop repaired the original Kindle Fire we had and so we use it for the GB to play games on and she has books that will themselves read to her and highlight the words as it reads.
I have a hard time reading any screen in direct sunlight other than the paper white screen. Not to mention the battery life on paper white is like 8 days or some ridiculous amount. Even in its case the paper white will slip in my back pocket like a paperback novel. (Just have to remember not to sit on it
)
Not to mention its pretty cool to finish a book at midnight, realize its a series and just order and start reading the next book in a matter of minutes.