I love my Kindle 3. But with that said, I'll also mentino that I have no experience with any other e-readers or e-book sellers besides Amazon.
I based my decision to buy a Kindle (as opposed to a Nook) on the opinions of my friends who have owned Kindles since their debut, and on my past experience with Amazon. It's hard telling just how the e-book world is going to unfold with respect to DRM, e-book sellers, inter-compatibility, library rentals etc. so I just jumped into the one that I felt most familiar with.
I prefer Kindle, but only because I actually own a Kindle. I read on my Droid at lunch, come home, my Kindle picks up where I left off and then I read on my Kindle. Works both ways, they both sync up with the furthest page read.