I adore my Kindle. I had to give up reading, except for craft books, because my vision is so screwed up. Kindle fixed that. You can adjust the spacing of the type and adjust the size instantly, making it easy to read. The screen also doesn't have the glare the other products have, which also helps.
The only caveat is that most library systems that offer ebooks are not yet Kindle compatible. However, since they have almost no offerings in my preferred genres (sci fi/fantasy ex), that's not an issue for me. A lot more people I know have the Nook or the Sony and they are perfectly happy with them (no vision issues). I've been told that Sony handles .pdf files better than Kindle. Nook is the only color one on the market just now, although I though I heard Sony was putting one out as well. Not a big deal for me, but is if you want children's books.
You CAN load .pdf files on the Kindle, but they are not as adjustable as I'd hoped they'd be. Hoping to fix that.
edited to add: even if price wasn't an issue, I'd still stick with Kindle because it is so much easier to deal with when you have vision problems. If your eyesight is really good, then I'd pick the one that best handles .pdf files. Also, ebooks will not replace craft books or even most cooking books, because you can't fit all the info on one page and still read it.