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.
I use my Android phone to read eBooks. The text is crisp and easy to read, even at very small font sizes. It's as light as a paperback book and fits easily in my pocket to facilitate reading on the go.
The only downside I have encountered is while in a plane I cannot read during takeoff or landing, but that would be true for any electronic book reader.
Others have commented over the past many years that they could not understand how I can view such small text on my PC monitors. Though in the last 10 years or so I have been having problems reading the fine print on some things, especially if there is little contrast between the letters and the background (reading the lettering on a wall wart is futile!). I do wear glasses, but only to correct near-sightedness. Usually wear them to drive (though a year ago I still passed the eye test at the DMV without my glasses), when sitting in a conference trying to see the projected slides, or when standing at the counter of a fast-food place trying to decide what I want. I don't wear them for computing - in fact I can't focus on the screen with them on.
My preference would be an ebook reader with colored e-ink (like the kindle etc) but probably an iPad as a second choice.
I tried the Android phone for a bit but didn't like it.
Not all eBook readers are touch screen, and in my opinion this is required.