Hmmm I have Nook Color, Phone, and Asus Transformer Tablet. I have used Kindle and original e-ink Nook.
I use my Android phone when on line, waiting at doc's office and else where on the go. It is pocket size and I always have it on me.
I use my Asus rarely for reading. I find it to be an awkward size, even though I can fit a lot more text per screen.
My clear favorite is the NookColor. Its about the size of some real books, can read Kindle, Nook, or any kind of ebook on it I want (well cept apple), works with out external light source, and all normal areas I would read in, etc.
I've played with the E-Inks, and yeah reading poolside with them might be great... but ehh... if Im by a pool, I'm jumping in not reading.
Battery life on e-ink is pretty cool, but honestly my NookColor goes long enough that it no longer matters...
tldr; Nook Color is my favorite general purpose reader.