Well I have an Astak Pocket Pro (5" screen), and it is my first ereader. I have done alot of research and kept my eye on the market since the Kindle 1 was released (I was really intrigued by the concept of an ereader). For me the PP is an absolute dream for reading novels, nothing I would change about it at all, comfortable to hold, I find I get about 2/3 of a normal paperback page on the screen at about the same font size, so not all that different, battery lasts forever, large choice of supported files.
Now my only current requirements for the next ereader is something I can use for Uni. It will have to be a 9.7" screen, offer PDF cropping, ability to have multiple files opened and switch between them. That is about it, my needs are very simple. I will probably never get one as I finish Uni in a year, so the money would be kind of wasted, I can't see myself reading for pleasure on a large screen reader.