I have a Sony PRS-700 and it is very good. eInk allows for great reading outdoors, but indoors tje contrast is not as good as it could get. The amazingly low power consumption makes is a very "green" product compared to LCD-based screens and you can read for sometimes 2-3 weeks without recharging.
That being said, the reason why I have one is more to use as a writer (reference books, classics, my own books to see how they look...) for proofreading. I normally have to print anywhere from 6 to 12 full copies of novels. With my current novel, I would be already at 3 copies (27$ each time), but instead I only printed it once (last Monday) and did my "reading as a reader" part on the Sony (which allows entering comments and notes). And for classics (which are free). It looks like nothing, but I read already novels that would have cost me about 60$ in cheap print.
So, my two cents here would be: avoid Kindle as you are 100% stuck with Amazon UNLESS they start supporting PDF and unless you REALLY WANT IT!
If at work you print a lot of documents, then the Sony might be a good bet as it supports RTF (automatic conversion when using Word documents), PDF and one or two other formats that are available either with DRM or not. BUT (and it is a big BUT), the eInk is not quite there yet unless you read a lot outside, have good eyes (mine are a bit dammaged) or great indoort lighting (halogen or some other "white spectrum" bulbs). So you might want to wait for a new generation.
Hoping I made any kind of sense!