None. The only ebook reader that will come anywhere close is the Kindle DX.
Better is a tablet or netbook, followed by a full size laptop or desktop. Generally, I read PDFs on my 17" laptop screen. Some (tagged PDFs) can be read on smaller screens with tolerable results. Both my K3 and my jetBook attempt to make PDFs not completely out of the question by various strategems, with varying degrees of success.