I have a Kindle and absolutely love it. It's far more comfortable to read on than anything else I've ever used. I have an iPhone 4, but even its "retina display" isn't as pleasant to look at for long periods of time. Sure, e-Ink is not in colour, but for a device on which you want to read lengthy pieces of text I wouldn't recommend anything else (and none of the paper novels I own are in colour either).
The battery also lasts very, very long if you turn the wi-fi off (with it on I need to charge about once every week under my normal usage of reading during my commute).
I went with the Kindle because for someone who doesn't have US creditcard buying eBooks is an incredible hassle. There's very few places that actually have any kind of decent agreement with a good number of international publisher, and I was lured into the Kindle store as it was the only place where I could actually buy a book I was looking for.