I'd also opt for the Sony.
A friend gave me his PRS-505. I find it to be fine. Not great but fine. No doubt the newer ones are nicer. The 505 reads ePub very well, handles PDF, works with the pilot Digital Editions Library service offered in my municipality (borrow eBooks for two weeks at a time.) It works well in Linux and Mac OS. Getting books on and off is a snap, just using drag and drop. Battery life is good. The Sony Reader store has a reasonable collection of books at a decent price. It's generally not cheaper than a print book from Amazon.ca but the format and selection is convenient for me. The old Sony eReader Store used a proprietary locked-down format that nothing else could handle. Thankfully, the new Sony Reader Store now sells books in ePub format.
Now, the ePub books sold at the Sony Store are DRM-encumbered. This, of course, is very bad. (See other comments for good examples of why.) Having said this, if you live in a country with sane fair dealing/fair use laws, you can, with a little work, find reasonably straightforward ways to remove the DRM from the books sold at the Reader Store.
Piracy is bad, so is treating your customers as thieves by default. I won't ever pirate a book; nor will I invest in a locked format that I can't use as I'd like. I buy almost all of my music on-line now because I can finally buy MP3 and AAC files without DRM. I won't buy into digital movies or Blu-Ray because of the DRM. I was very reluctant to buy into electronic books until a I had a good source of DRM-free ePub books.
Thankfully, publishers seem to be getting this faster than the music and movie studios. Pretty much all O'Reilly books are now available as ePub. The Sony Reader Store sells ePub that you can eventually turn in to standard DRM-free books. The situation appears to be getting better. One can now read books purchased through the Sony Reader Store in Linux and with ePub software for phones. The situation with Sony reminds me of iTunes pre-M4A. Yes, you could buy an album electronically but you had to burn it out and rip it back to side-step the DRM. Not terribly user-friendly but not horrible.
To me, the worst thing about eBook readers is that vendors are locking customers in to closed silos. A Nook can't read Kindle books, Kindle can't read the ubiquitous ePub format. All the while, you can walk down to the store and buy the print version without any of these limitations for about the same price. This is madness.
Privacy concerns are also a problem. The thought of a device, with an always-on wired connection, allowing companies to remove books post-purchase scares me. The thought of Amazon knowing what page I am on of every book they sell me also bothers me. In all of this, Sony, of all companies, looks the least bad. Go figure.
No doubt it's early days. I think you'd be nuts to buy anything that can't handle ePub and PDF. I also wouldn't buy anything that locks me to a single supplier of books.