Hmmm... it is a hard question. I own a PRS-650 and am very happy with it. Previously I had a PRS-505 and a 6" screen became a default size for me. The card slot is also convenient if you want to get a quick copy of non-DRMed content. However, it is also tempting to buy a PRS-350 because it looks so compact and easy to carry around for casual reading.