I had my iPad as an only ereader, for a few months, in between iLiad and Kindle. The reading-experience of everything was good on it, especially for the PDF and magazines.
But overall, for quiet reading and reflecting, the iPad or any other colourscreen with lots of options, would be too much of an experience for me. I just kept reading-browsing-reading......
So I'm fine with the Kindle for reading; would love to see the frontcover as first page, and am waiting for a better PDF-performance.
I don't think I would buy a Nook with colourscreen.