I'm sort of in the business (work for a publisher, have played with Kindle and iPad, read books on a Sony). The Sony can view PDFs (but I'm not sure you'd want to, unless the PDF is designed for a very small screen, and is black and white – e-Ink screen *very* slow for greyscale images), not sure about the Kindle.
If you have to buy one right now, I'd say Sony Reader rather than Kindle – now that Apple have adopted it for the iPad, it feels like ePub is going to become the 'standard' format, rather than Amazon's proprietary whatever it's called format. I think go for the touch screen one – any e-book reader that doesn't have a touch screen is going look so backward at the end of this month when Apple launch the iPad, and the ergonomics on the Sony with buttons and the Kindle leave a lot to be desired.
It may also be the case that any e-book reader that has an e-Ink screen (Sony, Kindle) is also going to look very slow and backward after the fast, very high res and full colour iPad – even though it makes the batteries last forever, I wouldn't want shares in e-Ink screen tech right now.
Or wait until the iPad is out, and then look for one of the older models on eBay (right now eBay prices are implausibly high, but iPad may change that).