I have the Paperwhite and an iPad mini. The Paperwhite is the most recently updated Kindle. The e- ink is excellent for reading out doors and does not cause eye strain. It looks very close to reading an actual book. The Paperwhite has an adjustable light similar to the Nook Glowlight that shines on the screen, but is not backlit like the iPad
I also enjoy reading on the iPad using the Kindle app. Both are great for reading on as you can adjust font size and brightness on both. With the Kindle app you can choose a white, black or sepia background for reading.
The Kindle app has more detailed info regarding each book: books in the series, characters, important places, quotes, notes for parents and summary. The covers of the books are in color on the iPad.
With the automatic sync you can read on one and pick right up on the other. I use both on a daily basis and enjoy each equally. On the kindle, there is no interruptions reading due to texts, notifications or e-mails. The battery life on the Kindle is great (2 weeks between charges, with wi-fi off)
If you read a lot of books and it's within your budget, I think having a dedicated e reader in addition to an iPad works out great.