Buying a kindle for reading PDF is a terrible idea,too small, slow and non colour, 5-6 inch e-ink readers were made to read mobi and epub format designed for that screensize.If you are just confusing PDF with regular fiction and non fiction ebooks, like the e-books sold on amazon then its fine, buy an e-ink reader, the nook simple touch is the current best value by far and the one to buy.If you want to read technicals pdf's, which are for large sized and more detailed books which feature pictures, graphs etc for things like computer programming, DIY etc then buy a 10inch tablet to read the PDF on, lots of good value Android tablets out now.
Edit:if you read a combination of regular and technical books, and have been reading them on your laptop, then just buy a tablet, will display both fine.