I have a Nook Simple Touch and a cheap Kindle. I love them both. I don't think you could go wrong with either, unless you have a strong preference for one store over the other.
Sometimes a book will be a little cheaper at Amazon, sometimes one will be a little cheaper at B&N, but usually they cost the same at both, particularly the well known ones. I think Amazon has the edge there, with more deals, but not so many that it's beyond the value of having $75 off an e-reader off the top due to gift cards.
Also, with nooks you can use an SD card so you can store a greater number of books, if you end up having a massive collection.
But I love my Kindle too and I can't speak badly about that. Either would be a good choice. I haven't seen the Paperwhite, but I'm quite happy with the old ones. You could go to a store and compare them to see if you prefer the screen enough to ignore the B&N cards and just get that.