I have both a nook and a Sony 650. The new firmware for the nook did bring many improvements to the nook, but I still prefer the Sony. Even though the screens are the same size, since the Sony doesn't have the LCD screen it's quite a bit smaller and lighter than the nook. It also has much better PDF support and better battery life.
I do like my nook and still use it on occasion, but the Sony is definitely my first choice as reader.
Good luck with your decision!
dordale