With the ebook business still being so DRM-heavy and divided into a small number of incompatible walled gardens, it’s important to invest in a device with the biggest content library and the parent company with the healthiest future. In this business, that has always been Amazon.
I agree if you are going to invest in ebooks, best to choose the company with the largest library and healthiest future. Personally, while I do purchase ebooks, I am certainly not going to build a significant library until these companies stop trying to hold us hostage on their platforms using proprietary formats and DRM.
When I purchase a book, I should be purchasing the license to that book and if new formats come out in the future, I should be able to upgrade for a nominal fee without having to repurchase something I already own. Media companies are fighting to keep this from happening — or something similar — that would stop them from charging us when our favorite books, music, movies or television shows change format.