I think it depends on how you intend to use it.
If you only want a reading device, then I think the Kindle stands far above the rest. Part of the reason is the "no-glare" screen. Keep in mind though, it is a reading only device at the moment and black/white.
However, if you want a more general purpose device, one that you can do more than just read books, magazines, newspapers, etc. on, then you'll want to look at one of the other devices.
So first decide exactly how you intend to use it and then how much you are willing to spend.
Not too helpful I know, but as you stated, this is subjective.