I had a Kindle 2 and sold it when I got an iPad.
One week in Cancun and the release of the new Kindle 6" screen has me wanting another Kindle.
I love my iPad. But when I want to read a book, I'd rather be holding a Kindle. It's smaller, lighter, and you can use it on the beach without overheating and/or becoming invisible. When wearing polarized glasses, the iPad screen disappears and it's poor in sunlight.
So for me, both. My birthday is Sunday, so I'm hoping I left enough hints.