I have had two Sony readers. I use the Sony software with it. But I also use Calibre with special tools that will strip the standard Adobe epub drm from my books. I then save them in an ebook file on my pc as well as on a backup hard drive.
Stripping the drm is the only way to truly ensure that I can keep my books. I am not a tech type person, but after reading of too many people losing their books either from not stripping them or not downloading the books in time before they disappeared from where ever they were originally bought from convinced me that this was a necessary step for me to take.
I had it all set up in Calibre in just a few minutes following the very clear instructions from Apprentice Alf and was then busy stripping my books that I can now load on ANY machine that I choose now and in the future.
There is no need to root the reader, Calibre & the tools take care of it quite painlessly.
I chose Sony because I didn't want to be tied to B&N, Amazon, Apple etc.
So pick whichever reader has the most features that you want, download Calibre & the tools then enjoy your reading.