If you are in the US, then there are three options that all use the same identical 6" E-Ink screen: Sony PRS-505, Bookeen Cybook, Amazon Kindle. The Sony has a newer screen controller and can do 8 level grey scale (vs 4 level in the other two). Page turns is the fastest available with E-Ink and should be comparable between the three. The Sony is the cheapest, and you can probably get it before Christmas (and see one in person first at a Border's bookstore). There is no compelling reason to pay more in your case for the others. Note that you will need to use the software from this site to convert many of your e-books for the Sony.
If you are outside the US, the Bookeen is probably your best choice - even though the lack of access to the Sony and Amazon e-books stores is not an issue for you.
None of these are very good with PDFs - you are much better off with a reflowable format. With a reflowable format, the 6" screen is big enough (and you can change the font size as needed, the larger the font the fewer words per page).