I'm a big advocate against PDF for any of the devices unless the PDF is made for a specific screen size it never looks good and then if you ever decide to get a device with a smaller or larger screen you'd have to recreate the file.

Right now at Mobile Read forums people are posting their experiences with the Nook I highly recommend reading the posts and seeing how it actually works. Based on what I read it still has a ways to go before becoming a better device. However, I have a Sony PRS-505 and I love it so I'm a bit biased.