The right e-reader for you depends on what your reading preferences are:
Do you prefer
print that resembles a traditional book? - then the e-ink models are best (like the Nook Simple Touch)
will u carry the e-reader around? - then something smaller and lighter would be better
read at night - choose one with a backlight
read during day and/or outside - choose a model that says "can read in daylight" - I'm not sure if the anti-glare like on the Kindle Fire HD means the same thing
Most models can view multiple types of formats including pdfs - but check the accepted format lists for the various readers.
I still love my Nook, Generation 1. I can read pdfs on it. The kindle app on my ipad is perfect for Amazon books.
Sorry not to give a specific answer, hopes this helps.