I have the first version of the kindle touch and really love how compact, handy and readable it is. I used it voraciously for about 6 months, but now my son uses it.
I currently have a galaxy s3 phone and use the kindle app on it for all my books. The kindle has a better, more readable screen. The kindle has better battery life. But, my GS3 is lighter than a kindle, easier to pack than my kindle, serves as my camera, serves as my phone, serves as backup navigation, and occasionally provides me internet access.
I used to have a phone with a 3.5" screen, but I found that too small to comfortably read on. For the last 2 years, I have been doing almost all of my reading on my GS3's 4.8" screen. And while the kindle screen is better to read on, I always have my phone with me and I find it far more convenient than using a separate device.
I have an upgraded 3000mAH battery on my phone. I still have charge to spare after a week long hike. But I usually leave the phone in airplane mode or off when I am backpacking to conserve battery.
I understand those who would prefer using the larger screen on a kindle device. But for me, I have found that I prefer using my convergence device.