I have a K2 and two K1's (my original K1 passed down my children when I upgraded to a K2, then bought another one because my children kept fighting over the original K1). I am thinking about selling the K1's now and replacing them with K3's, plus adding another K3 for my youngest, who is now reading chapter books and is insisting that she's a big girl now and needs her own Kindle.
I also have an iPad, but I didn't purchase it as an ebook reader (although I do use it as one from time to time; I very much prefer my Kindle, though).