I have a Kindle e-ink, but these days I mostly use my Kindle Fire HD for reading books. I do notice the e-ink is a bit more relaxing on the eyes, but I'm not really bothered by reading on the LCD.
From time to time I use my Nexus 4 to reading (I don't own an iPhone) and I enjoyed reading on that too. The main negative is I have to change pages more frequently. Also I wish the Kindle app would let me change pages with the volume button (perhaps the iPhone version does, they skimp on the Android version).