Well, the Sony Pocket reader has the new Pearl screen and I believe it has a higher resolution as well, so it should be easier to read from. It is quite a bit smaller and lighter than the Nook, which is a pro for those who want something that will fit in their pocket, but a con for those who want a larger screen (5 inch vs. 6 inch). The Sony reader comes with 12 dictionaries included on the device. It doesn't have any sort of internet connection, so you have to side load books. To me, that's not a big deal at all - in fact, I drag and drop most of my books onto my Sony 505 as if it were a usb. Others swear by wi-fi and 3g equipped readers, so YMMV.
The Sony seems (from online video reviews that I've seen) to be very easy to use, and I believe that it has a longer battery than the Nook, but with the Nook you get BN's bookstore. Sony seems to be the best (non 9.7 inch) device at rendering PDFs, from what I've heard, so that's something to take into consideration as well. You can annotate and use dictionaries on PDFs with the Sony devices.
Try looking up some video reviews on youtube, I find that the longer reviews tend to be quite well done. Also, check out this site:
http://www.the-ebook-reader.com/
They have really great reviews, often accompanied by a video.