[WalkingDistance]

Well I was debating the same thing when I got my kindle. I didn't know which device to get so I mapped out what I wanted an e-reader for:
-e-ink display (LCD hurts my eyes)
-Cheap (within reason... i'd say 200 or below)
-Battery Life (small factor, but i don't want to worry about recharging during long trips)
-support/users (Kindle has a HUGE userbase. I would argue that it's larger than any other ebook reader. Because of the userbase, the support that the company would provide would be, in principle but not always the case, better)

I mainly wanted an ebook reader for novels (not journals or periodicals or children's books) so I felt the kindle 3 was the best for me.

It has the e-ink pearl display (although sony has one now too). It was cheap (cheaper than sony). The battery life was advertised to be a month! I've never heard of any electronic lasting a month! so that was a definite plus. Kindles have a huge userbase (as evident from this forum). Support is awesome (I got my first kindle replaced VERY easily).

Sony has those cool new touchscreen things now. Personally, I don't have a use/need for one so if that's what you're looking for, that's one thing (that i can point out off the top of my head) that sony has over the kindle.

That's what i went through in my decision-making. Hope that helps.

Also Kindles seem to have some level of inconsistency in screen quality (contrast) and build. This could be due to bad manufacturing/lack of good quality control or due to the large volume of kindles that are shipped out/created.

But not to stray from the original point, whispersync is a really great service.

Kindles don't natively support epub (unless you jailbreak and do stuff to it, i don't know if you're willing to tinker around with your device). However, converting through calibre is really fast and easy.