If you want a 6 inch screen and you plan on reading many PDFs, you should check out the Sony PRS-650, it seems to handle PDFs much better than the Kindle 3. Here is a PDF review. It's pricier than the Kindle (about $220 USD), but worth it (imho) if you plan on reading many PDFs. You can also mark up the PDFs using the stylus.
http://www.youtube.com/watch?v=co5bP...eature=channel