[fjtorres]

The available content is *not* the same for all devices.
Some ebooks and magazines are only available on tablets and audiobooks are only available on readers with audio or on tablets. And on tablets they typically need a separate app.
The vast majority of files will be available everywhere but there will be exceptions.

Decide first what, how, and where you will be reading and which tradeoffs make sense for you; weight, battery life, outdoor readability, color, audio, etc.