During the week I commute by train between home and work. I also travel for work and spend a good amount of time in airports and airplanes. I like having the convenience of multiple apps in one device, which makes my iPad and iPhone very convenient.
I have not been a Kindle user as a stand alone device, but I like the size of the Kindle Fire and find it works much better for commuting than the iPad. The screen size on the Kindle Fire is great for reading, to play games and music. However, I prefer the screen size of the iPad for watching movies over the Kindle Fire.
If I want to go relax at a coffee shop to read and listen to music I would prefer working with the Kindle Fire. But, if I want to be productive and work at the same coffee shop I will take my iPad.