I can attest that the Kindle Fire is a perfect reading device. Perfect form factor, light yet feels great, etc. I really don't think an iPad is great for reading based on size, but I've never had one long enough to try it.
I had a Fire and really didn't like it for reading -- it falls in the valley of uselessness between a Kindle (DX being my favorite) and the iPad. I don't find my iPad 1 particularly heavy -- the main drawback of the iPad vs. Kindles is lack of daylight readability, and to a lesser degree, potentially distracting apps (email, web).
The Fire seems like a great video watching device, but I don't do much of that (and when I do, it's on a projector with surround sound and other people)
Quite on point. Few people would willingly admit to this, but a lot of research suggests that simply having options available imposes a real cognitive load. Simple additions to text like footnotes and hyperlinks produce real drops in recall/comprehension - it's not a stretch to apply this to the iPad with its notifications and rich entertainment options.
The Fire seems like a great video watching device, but I don't do much of that (and when I do, it's on a projector with surround sound and other people)